diff --git a/go.mod b/go.mod
index 51caf33..a404c3e 100644
--- a/go.mod
+++ b/go.mod
@@ -66,6 +66,7 @@ require (
 	github.com/go-openapi/validate v0.24.0 // indirect
 	github.com/go-playground/locales v0.14.1 // indirect
 	github.com/go-playground/universal-translator v0.18.1 // indirect
+	github.com/go-redis/redismock/v9 v9.2.0 // indirect
 	github.com/go-sql-driver/mysql v1.9.3 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // indirect
 	github.com/golang-jwt/jwt/v4 v4.5.2 // indirect
diff --git a/go.sum b/go.sum
index 85f8f0a..6b60f75 100644
--- a/go.sum
+++ b/go.sum
@@ -152,6 +152,8 @@ github.com/go-playground/universal-translator v0.18.1 h1:Bcnm0ZwsGyWbCzImXv+pAJn
 github.com/go-playground/universal-translator v0.18.1/go.mod h1:xekY+UJKNuX9WP91TpwSH2VMlDf28Uj24BCp08ZFTUY=
 github.com/go-playground/validator/v10 v10.27.0 h1:w8+XrWVMhGkxOaaowyKH35gFydVHOvC0/uWoy2Fzwn4=
 github.com/go-playground/validator/v10 v10.27.0/go.mod h1:I5QpIEbmr8On7W0TktmJAumgzX4CA1XNl4ZmDuVHKKo=
+github.com/go-redis/redismock/v9 v9.2.0 h1:ZrMYQeKPECZPjOj5u9eyOjg8Nnb0BS9lkVIZ6IpsKLw=
+github.com/go-redis/redismock/v9 v9.2.0/go.mod h1:18KHfGDK4Y6c2R0H38EUGWAdc7ZQS9gfYxc94k7rWT0=
 github.com/go-sql-driver/mysql v1.9.3 h1:U/N249h2WzJ3Ukj8SowVFjdtZKfu9vlLZxjPXV1aweo=
 github.com/go-sql-driver/mysql v1.9.3/go.mod h1:qn46aNg1333BRMNU69Lq93t8du/dwxI64Gl8i5p1WMU=
 github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/melR3HDY=
diff --git a/internal/adapters/graphql/auth_mutations_test.go b/internal/adapters/graphql/auth_mutations_test.go
new file mode 100644
index 0000000..680ffb6
--- /dev/null
+++ b/internal/adapters/graphql/auth_mutations_test.go
@@ -0,0 +1,113 @@
+package graphql_test
+
+import (
+	"context"
+	"os"
+	"testing"
+	"tercul/internal/adapters/graphql"
+	"tercul/internal/app/auth"
+	"tercul/internal/domain"
+	platform_auth "tercul/internal/platform/auth"
+	"tercul/internal/testutil"
+
+	"github.com/stretchr/testify/suite"
+)
+
+type AuthMutationTestSuite struct {
+	testutil.IntegrationTestSuite
+	resolver graphql.MutationResolver
+}
+
+func TestAuthMutations(t *testing.T) {
+	suite.Run(t, new(AuthMutationTestSuite))
+}
+
+func (s *AuthMutationTestSuite) SetupSuite() {
+	s.IntegrationTestSuite.SetupSuite(&testutil.TestConfig{
+		DBPath: "auth_mutations_test.db",
+	})
+}
+
+func (s *AuthMutationTestSuite) TearDownSuite() {
+	s.IntegrationTestSuite.TearDownSuite()
+	os.Remove("auth_mutations_test.db")
+}
+
+func (s *AuthMutationTestSuite) SetupTest() {
+	s.IntegrationTestSuite.SetupTest()
+	s.resolver = (&graphql.Resolver{App: s.App}).Mutation()
+}
+
+func (s *AuthMutationTestSuite) TestChangePassword() {
+	// Helper to create a user for tests
+	createUser := func(username, email, password string) *domain.User {
+		resp, err := s.App.Auth.Commands.Register(context.Background(), auth.RegisterInput{
+			Username: username,
+			Email:    email,
+			Password: password,
+		})
+		s.Require().NoError(err)
+		return resp.User
+	}
+
+	// Helper to create a context with JWT claims
+	contextWithClaims := func(user *domain.User) context.Context {
+		return testutil.ContextWithClaims(context.Background(), &platform_auth.Claims{
+			UserID: user.ID,
+			Role:   string(user.Role),
+		})
+	}
+
+	s.Run("Success", func() {
+		// Arrange
+		initialPassword := "password123"
+		newPassword := "newPassword456"
+		user := createUser("testuser-changepw", "testuser.changepw@test.com", initialPassword)
+		ctx := contextWithClaims(user)
+
+		// Act
+		success, err := s.resolver.ChangePassword(ctx, initialPassword, newPassword)
+
+		// Assert
+		s.Require().NoError(err)
+		s.True(success)
+
+		// Verify the password change by trying to log in with the new and old passwords
+		_, err = s.App.Auth.Commands.Login(context.Background(), auth.LoginInput{Email: user.Email, Password: newPassword})
+		s.NoError(err, "Login with new password should succeed")
+
+		_, err = s.App.Auth.Commands.Login(context.Background(), auth.LoginInput{Email: user.Email, Password: initialPassword})
+		s.Error(err, "Login with old password should fail")
+		s.ErrorIs(err, auth.ErrInvalidCredentials)
+	})
+
+	s.Run("Incorrect current password", func() {
+		// Arrange
+		initialPassword := "password123"
+		newPassword := "newPassword456"
+		user := createUser("testuser-wrongpw", "testuser.wrongpw@test.com", initialPassword)
+		ctx := contextWithClaims(user)
+
+		// Act
+		success, err := s.resolver.ChangePassword(ctx, "wrong-password", newPassword)
+
+		// Assert
+		s.Require().Error(err)
+		s.False(success)
+		s.ErrorIs(err, auth.ErrInvalidCredentials)
+
+		// Verify the password was not changed
+		_, loginErr := s.App.Auth.Commands.Login(context.Background(), auth.LoginInput{Email: user.Email, Password: initialPassword})
+		s.NoError(loginErr, "Login with original password should still succeed")
+	})
+
+	s.Run("Unauthenticated user", func() {
+		// Act
+		success, err := s.resolver.ChangePassword(context.Background(), "any-password", "any-new-password")
+
+		// Assert
+		s.Require().Error(err)
+		s.False(success)
+		s.ErrorIs(err, domain.ErrUnauthorized)
+	})
+}
\ No newline at end of file
diff --git a/internal/adapters/graphql/user_mutations_test.go b/internal/adapters/graphql/user_mutations_test.go
new file mode 100644
index 0000000..5d3c0bf
--- /dev/null
+++ b/internal/adapters/graphql/user_mutations_test.go
@@ -0,0 +1,218 @@
+package graphql_test
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"testing"
+	"tercul/internal/adapters/graphql"
+	"tercul/internal/adapters/graphql/model"
+	"tercul/internal/app/auth"
+	"tercul/internal/domain"
+	platform_auth "tercul/internal/platform/auth"
+	"tercul/internal/testutil"
+
+	"github.com/stretchr/testify/suite"
+)
+
+type UserMutationTestSuite struct {
+	testutil.IntegrationTestSuite
+	resolver graphql.MutationResolver
+}
+
+func TestUserMutations(t *testing.T) {
+	suite.Run(t, new(UserMutationTestSuite))
+}
+
+func (s *UserMutationTestSuite) SetupSuite() {
+	s.IntegrationTestSuite.SetupSuite(&testutil.TestConfig{
+		DBPath: "user_mutations_test.db",
+	})
+}
+
+func (s *UserMutationTestSuite) TearDownSuite() {
+	s.IntegrationTestSuite.TearDownSuite()
+	os.Remove("user_mutations_test.db")
+}
+
+func (s *UserMutationTestSuite) SetupTest() {
+	s.IntegrationTestSuite.SetupTest()
+	s.resolver = (&graphql.Resolver{App: s.App}).Mutation()
+}
+
+// Helper to create a user for tests
+func (s *UserMutationTestSuite) createUser(username, email, password string, role domain.UserRole) *domain.User {
+	resp, err := s.App.Auth.Commands.Register(context.Background(), auth.RegisterInput{
+		Username: username,
+		Email:    email,
+		Password: password,
+	})
+	s.Require().NoError(err)
+
+	user, err := s.App.User.Queries.User(context.Background(), resp.User.ID)
+	s.Require().NoError(err)
+
+	if role != user.Role {
+		user.Role = role
+		err = s.DB.Save(user).Error
+		s.Require().NoError(err)
+	}
+	return user
+}
+
+// Helper to create a context with JWT claims
+func (s *UserMutationTestSuite) contextWithClaims(user *domain.User) context.Context {
+	return testutil.ContextWithClaims(context.Background(), &platform_auth.Claims{
+		UserID: user.ID,
+		Role:   string(user.Role),
+	})
+}
+
+func (s *UserMutationTestSuite) TestDeleteUser() {
+	s.Run("Success as admin", func() {
+		// Arrange
+		adminUser := s.createUser("admin_deleter", "admin_deleter@test.com", "password123", domain.UserRoleAdmin)
+		userToDelete := s.createUser("user_to_delete", "user_to_delete@test.com", "password123", domain.UserRoleReader)
+		ctx := s.contextWithClaims(adminUser)
+		userIDToDeleteStr := fmt.Sprintf("%d", userToDelete.ID)
+
+		// Act
+		deleted, err := s.resolver.DeleteUser(ctx, userIDToDeleteStr)
+
+		// Assert
+		s.Require().NoError(err)
+		s.True(deleted)
+
+		// Verify user is deleted from DB
+		_, err = s.App.User.Queries.User(context.Background(), userToDelete.ID)
+		s.Require().Error(err)
+		s.Contains(err.Error(), "entity not found", "Expected user to be not found after deletion")
+	})
+
+	s.Run("Success as self", func() {
+		// Arrange
+		userToDelete := s.createUser("user_to_delete_self", "user_to_delete_self@test.com", "password123", domain.UserRoleReader)
+		ctx := s.contextWithClaims(userToDelete)
+		userIDToDeleteStr := fmt.Sprintf("%d", userToDelete.ID)
+
+		// Act
+		deleted, err := s.resolver.DeleteUser(ctx, userIDToDeleteStr)
+
+		// Assert
+		s.Require().NoError(err)
+		s.True(deleted)
+
+		// Verify user is deleted from DB
+		_, err = s.App.User.Queries.User(context.Background(), userToDelete.ID)
+		s.Require().Error(err)
+		s.Contains(err.Error(), "entity not found", "Expected user to be not found after deletion")
+	})
+
+	s.Run("Forbidden as other user", func() {
+		// Arrange
+		otherUser := s.createUser("other_user_deleter", "other_user_deleter@test.com", "password123", domain.UserRoleReader)
+		userToDelete := s.createUser("user_to_be_kept", "user_to_be_kept@test.com", "password123", domain.UserRoleReader)
+		ctx := s.contextWithClaims(otherUser)
+		userIDToDeleteStr := fmt.Sprintf("%d", userToDelete.ID)
+
+		// Act
+		deleted, err := s.resolver.DeleteUser(ctx, userIDToDeleteStr)
+
+		// Assert
+		s.Require().Error(err)
+		s.False(deleted)
+		s.True(errors.Is(err, domain.ErrForbidden))
+	})
+
+	s.Run("Invalid user ID", func() {
+		// Arrange
+		adminUser := s.createUser("admin_deleter_2", "admin_deleter_2@test.com", "password123", domain.UserRoleAdmin)
+		ctx := s.contextWithClaims(adminUser)
+
+		// Act
+		deleted, err := s.resolver.DeleteUser(ctx, "invalid-id")
+
+		// Assert
+		s.Require().Error(err)
+		s.False(deleted)
+		s.True(errors.Is(err, domain.ErrValidation))
+	})
+
+	s.Run("User not found", func() {
+		// Arrange
+		adminUser := s.createUser("admin_deleter_3", "admin_deleter_3@test.com", "password123", domain.UserRoleAdmin)
+		ctx := s.contextWithClaims(adminUser)
+		nonExistentID := "999999"
+
+		// Act
+		deleted, err := s.resolver.DeleteUser(ctx, nonExistentID)
+
+		// Assert
+		s.Require().Error(err)
+		s.False(deleted)
+		s.Contains(err.Error(), "entity not found", "Expected entity not found error for non-existent user")
+	})
+}
+
+func (s *UserMutationTestSuite) TestUpdateProfile() {
+	s.Run("Success", func() {
+		// Arrange
+		user := s.createUser("profile_user", "profile.user@test.com", "password123", domain.UserRoleReader)
+		ctx := s.contextWithClaims(user)
+
+		newFirstName := "John"
+		newLastName := "Doe"
+		newBio := "This is my new bio."
+		input := model.UserInput{
+			FirstName: &newFirstName,
+			LastName:  &newLastName,
+			Bio:       &newBio,
+		}
+
+		// Act
+		updatedUser, err := s.resolver.UpdateProfile(ctx, input)
+
+		// Assert
+		s.Require().NoError(err)
+		s.Require().NotNil(updatedUser)
+		s.Equal(newFirstName, *updatedUser.FirstName)
+		s.Equal(newLastName, *updatedUser.LastName)
+		s.Equal(newBio, *updatedUser.Bio)
+
+		// Verify in DB
+		dbUser, err := s.App.User.Queries.User(context.Background(), user.ID)
+		s.Require().NoError(err)
+		s.Equal(newFirstName, dbUser.FirstName)
+		s.Equal(newLastName, dbUser.LastName)
+		s.Equal(newBio, dbUser.Bio)
+	})
+
+	s.Run("Unauthenticated user", func() {
+		// Arrange
+		newFirstName := "Jane"
+		input := model.UserInput{FirstName: &newFirstName}
+
+		// Act
+		_, err := s.resolver.UpdateProfile(context.Background(), input)
+
+		// Assert
+		s.Require().Error(err)
+		s.ErrorIs(err, domain.ErrUnauthorized)
+	})
+
+	s.Run("Invalid country ID", func() {
+		// Arrange
+		user := s.createUser("profile_user_invalid", "profile.user.invalid@test.com", "password123", domain.UserRoleReader)
+		ctx := s.contextWithClaims(user)
+		invalidCountryID := "not-a-number"
+		input := model.UserInput{CountryID: &invalidCountryID}
+
+		// Act
+		_, err := s.resolver.UpdateProfile(ctx, input)
+
+		// Assert
+		s.Require().Error(err)
+		s.Contains(err.Error(), "invalid country ID")
+	})
+}
\ No newline at end of file
diff --git a/internal/app/analytics/service.go b/internal/app/analytics/service.go
index 87bbcb2..feac04c 100644
--- a/internal/app/analytics/service.go
+++ b/internal/app/analytics/service.go
@@ -40,6 +40,7 @@ type Service interface {
 	UpdateUserEngagement(ctx context.Context, userID uint, eventType string) error
 	UpdateTrending(ctx context.Context) error
 	GetTrendingWorks(ctx context.Context, timePeriod string, limit int) ([]*domain.Work, error)
+	UpdateWorkStats(ctx context.Context, workID uint, stats domain.WorkStats) error
 }
 
 type service struct {
@@ -314,6 +315,12 @@ func (s *service) GetTrendingWorks(ctx context.Context, timePeriod string, limit
 	return s.repo.GetTrendingWorks(ctx, timePeriod, limit)
 }
 
+func (s *service) UpdateWorkStats(ctx context.Context, workID uint, stats domain.WorkStats) error {
+	ctx, span := s.tracer.Start(ctx, "UpdateWorkStats")
+	defer span.End()
+	return s.repo.UpdateWorkStats(ctx, workID, stats)
+}
+
 func (s *service) UpdateTrending(ctx context.Context) error {
 	ctx, span := s.tracer.Start(ctx, "UpdateTrending")
 	defer span.End()
diff --git a/internal/app/work/commands.go b/internal/app/work/commands.go
index 0279d81..26de6e4 100644
--- a/internal/app/work/commands.go
+++ b/internal/app/work/commands.go
@@ -305,14 +305,18 @@ func mergeWorkStats(tx *gorm.DB, sourceWorkID, targetWorkID uint) error {
 		return nil
 	}
 
+	// Store the original ID to delete later, as the sourceStats.ID might be overwritten.
+	originalSourceStatsID := sourceStats.ID
+
 	var targetStats domain.WorkStats
 	err = tx.Where("work_id = ?", targetWorkID).First(&targetStats).Error
 
 	if errors.Is(err, gorm.ErrRecordNotFound) {
-		// If target has no stats, create new ones based on source stats.
-		sourceStats.ID = 0 // Let GORM create a new record
-		sourceStats.WorkID = targetWorkID
-		if err = tx.Create(&sourceStats).Error; err != nil {
+		// If target has no stats, create a new stats record for it.
+		newStats := sourceStats
+		newStats.ID = 0
+		newStats.WorkID = targetWorkID
+		if err = tx.Create(&newStats).Error; err != nil {
 			return fmt.Errorf("failed to create new target stats: %w", err)
 		}
 	} else if err != nil {
@@ -325,8 +329,8 @@ func mergeWorkStats(tx *gorm.DB, sourceWorkID, targetWorkID uint) error {
 		}
 	}
 
-	// Delete the old source stats
-	if err = tx.Delete(&domain.WorkStats{}, sourceStats.ID).Error; err != nil {
+	// Delete the old source stats using the stored original ID.
+	if err = tx.Delete(&domain.WorkStats{}, originalSourceStatsID).Error; err != nil {
 		return fmt.Errorf("failed to delete source work stats: %w", err)
 	}
 
diff --git a/internal/app/work/commands_test.go b/internal/app/work/commands_test.go
index cdb6a2b..eb5d055 100644
--- a/internal/app/work/commands_test.go
+++ b/internal/app/work/commands_test.go
@@ -70,7 +70,7 @@ func (s *WorkCommandsSuite) TestCreateWork_RepoError() {
 }
 
 func (s *WorkCommandsSuite) TestUpdateWork_Success() {
-	ctx := platform_auth.ContextWithAdminUser(context.Background(), 1)
+	ctx := context.WithValue(context.Background(), platform_auth.ClaimsContextKey, &platform_auth.Claims{UserID: 1, Role: string(domain.UserRoleAdmin)})
 	work := &domain.Work{Title: "Test Work", TranslatableModel: domain.TranslatableModel{Language: "en"}}
 	work.ID = 1
 
@@ -111,17 +111,40 @@ func (s *WorkCommandsSuite) TestUpdateWork_EmptyLanguage() {
 }
 
 func (s *WorkCommandsSuite) TestUpdateWork_RepoError() {
+	ctx := context.WithValue(context.Background(), platform_auth.ClaimsContextKey, &platform_auth.Claims{UserID: 1, Role: string(domain.UserRoleAdmin)})
 	work := &domain.Work{Title: "Test Work", TranslatableModel: domain.TranslatableModel{Language: "en"}}
 	work.ID = 1
 	s.repo.updateFunc = func(ctx context.Context, w *domain.Work) error {
 		return errors.New("db error")
 	}
-	err := s.commands.UpdateWork(context.Background(), work)
+	err := s.commands.UpdateWork(ctx, work)
 	assert.Error(s.T(), err)
 }
 
+func (s *WorkCommandsSuite) TestUpdateWork_Forbidden() {
+	ctx := context.WithValue(context.Background(), platform_auth.ClaimsContextKey, &platform_auth.Claims{UserID: 2, Role: string(domain.UserRoleReader)}) // Not an admin
+	work := &domain.Work{Title: "Test Work", TranslatableModel: domain.TranslatableModel{Language: "en"}}
+	work.ID = 1
+
+	s.repo.isAuthorFunc = func(ctx context.Context, workID uint, authorID uint) (bool, error) {
+		return false, nil // User is not an author
+	}
+
+	err := s.commands.UpdateWork(ctx, work)
+	assert.Error(s.T(), err)
+	assert.True(s.T(), errors.Is(err, domain.ErrForbidden))
+}
+
+func (s *WorkCommandsSuite) TestUpdateWork_Unauthorized() {
+	work := &domain.Work{Title: "Test Work", TranslatableModel: domain.TranslatableModel{Language: "en"}}
+	work.ID = 1
+	err := s.commands.UpdateWork(context.Background(), work) // No user in context
+	assert.Error(s.T(), err)
+	assert.True(s.T(), errors.Is(err, domain.ErrUnauthorized))
+}
+
 func (s *WorkCommandsSuite) TestDeleteWork_Success() {
-	ctx := platform_auth.ContextWithAdminUser(context.Background(), 1)
+	ctx := context.WithValue(context.Background(), platform_auth.ClaimsContextKey, &platform_auth.Claims{UserID: 1, Role: string(domain.UserRoleAdmin)})
 	work := &domain.Work{Title: "Test Work", TranslatableModel: domain.TranslatableModel{Language: "en"}}
 	work.ID = 1
 
@@ -142,13 +165,27 @@ func (s *WorkCommandsSuite) TestDeleteWork_ZeroID() {
 }
 
 func (s *WorkCommandsSuite) TestDeleteWork_RepoError() {
+	ctx := context.WithValue(context.Background(), platform_auth.ClaimsContextKey, &platform_auth.Claims{UserID: 1, Role: string(domain.UserRoleAdmin)})
 	s.repo.deleteFunc = func(ctx context.Context, id uint) error {
 		return errors.New("db error")
 	}
-	err := s.commands.DeleteWork(context.Background(), 1)
+	err := s.commands.DeleteWork(ctx, 1)
 	assert.Error(s.T(), err)
 }
 
+func (s *WorkCommandsSuite) TestDeleteWork_Forbidden() {
+	ctx := context.WithValue(context.Background(), platform_auth.ClaimsContextKey, &platform_auth.Claims{UserID: 2, Role: string(domain.UserRoleReader)}) // Not an admin
+	err := s.commands.DeleteWork(ctx, 1)
+	assert.Error(s.T(), err)
+	assert.True(s.T(), errors.Is(err, domain.ErrForbidden))
+}
+
+func (s *WorkCommandsSuite) TestDeleteWork_Unauthorized() {
+	err := s.commands.DeleteWork(context.Background(), 1) // No user in context
+	assert.Error(s.T(), err)
+	assert.True(s.T(), errors.Is(err, domain.ErrUnauthorized))
+}
+
 func (s *WorkCommandsSuite) TestAnalyzeWork_Success() {
 	work := &domain.Work{
 		TranslatableModel: domain.TranslatableModel{BaseModel: domain.BaseModel{ID: 1}},
@@ -221,82 +258,157 @@ func TestMergeWork_Integration(t *testing.T) {
 	analyticsSvc := &mockAnalyticsService{}
 	commands := NewWorkCommands(workRepo, searchClient, authzSvc, analyticsSvc)
 
+	// Provide a realistic implementation for the GetOrCreateWorkStats mock
+	analyticsSvc.getOrCreateWorkStatsFunc = func(ctx context.Context, workID uint) (*domain.WorkStats, error) {
+		var stats domain.WorkStats
+		if err := db.Where(domain.WorkStats{WorkID: workID}).FirstOrCreate(&stats).Error; err != nil {
+			return nil, err
+		}
+		return &stats, nil
+	}
+
 	// --- Seed Data ---
-	author1 := &domain.Author{Name: "Author One"}
-	db.Create(author1)
-	author2 := &domain.Author{Name: "Author Two"}
-	db.Create(author2)
+	t.Run("Success", func(t *testing.T) {
+		author1 := &domain.Author{Name: "Author One"}
+		db.Create(author1)
+		author2 := &domain.Author{Name: "Author Two"}
+		db.Create(author2)
 
-	tag1 := &domain.Tag{Name: "Tag One"}
-	db.Create(tag1)
-	tag2 := &domain.Tag{Name: "Tag Two"}
-	db.Create(tag2)
+		tag1 := &domain.Tag{Name: "Tag One"}
+		db.Create(tag1)
+		tag2 := &domain.Tag{Name: "Tag Two"}
+		db.Create(tag2)
 
-	sourceWork := &domain.Work{
-		TranslatableModel: domain.TranslatableModel{Language: "en"},
-		Title:             "Source Work",
-		Authors:           []*domain.Author{author1},
-		Tags:              []*domain.Tag{tag1},
-	}
-	db.Create(sourceWork)
-	db.Create(&domain.Translation{Title: "Source English", Language: "en", TranslatableID: sourceWork.ID, TranslatableType: "works"})
-	db.Create(&domain.Translation{Title: "Source French", Language: "fr", TranslatableID: sourceWork.ID, TranslatableType: "works"})
-	db.Create(&domain.WorkStats{WorkID: sourceWork.ID, Views: 10, Likes: 5})
-
-	targetWork := &domain.Work{
-		TranslatableModel: domain.TranslatableModel{Language: "en"},
-		Title:             "Target Work",
-		Authors:           []*domain.Author{author2},
-		Tags:              []*domain.Tag{tag2},
-	}
-	db.Create(targetWork)
-	db.Create(&domain.Translation{Title: "Target English", Language: "en", TranslatableID: targetWork.ID, TranslatableType: "works"})
-	db.Create(&domain.WorkStats{WorkID: targetWork.ID, Views: 20, Likes: 10})
-
-	// --- Execute Merge ---
-	ctx := platform_auth.ContextWithAdminUser(context.Background(), 1)
-	err = commands.MergeWork(ctx, sourceWork.ID, targetWork.ID)
-	assert.NoError(t, err)
-
-	// --- Assertions ---
-	// 1. Source work should be deleted
-	var deletedWork domain.Work
-	err = db.First(&deletedWork, sourceWork.ID).Error
-	assert.Error(t, err)
-	assert.True(t, errors.Is(err, gorm.ErrRecordNotFound))
-
-	// 2. Target work should have merged data
-	var finalTargetWork domain.Work
-	db.Preload("Translations").Preload("Authors").Preload("Tags").First(&finalTargetWork, targetWork.ID)
-
-	assert.Len(t, finalTargetWork.Translations, 2, "Should have two translations after merge")
-	foundEn := false
-	foundFr := false
-	for _, tr := range finalTargetWork.Translations {
-		if tr.Language == "en" {
-			foundEn = true
-			assert.Equal(t, "Target English", tr.Title, "Should keep target's English translation")
+		sourceWork := &domain.Work{
+			TranslatableModel: domain.TranslatableModel{Language: "en"},
+			Title:             "Source Work",
+			Authors:           []*domain.Author{author1},
+			Tags:              []*domain.Tag{tag1},
 		}
-		if tr.Language == "fr" {
-			foundFr = true
-			assert.Equal(t, "Source French", tr.Title, "Should merge source's French translation")
+		db.Create(sourceWork)
+		db.Create(&domain.Translation{Title: "Source English", Language: "en", TranslatableID: sourceWork.ID, TranslatableType: "works"})
+		db.Create(&domain.Translation{Title: "Source French", Language: "fr", TranslatableID: sourceWork.ID, TranslatableType: "works"})
+		db.Create(&domain.WorkStats{WorkID: sourceWork.ID, Views: 10, Likes: 5})
+
+		targetWork := &domain.Work{
+			TranslatableModel: domain.TranslatableModel{Language: "en"},
+			Title:             "Target Work",
+			Authors:           []*domain.Author{author2},
+			Tags:              []*domain.Tag{tag2},
 		}
-	}
-	assert.True(t, foundEn, "English translation should be present")
-	assert.True(t, foundFr, "French translation should be present")
+		db.Create(targetWork)
+		db.Create(&domain.Translation{Title: "Target English", Language: "en", TranslatableID: targetWork.ID, TranslatableType: "works"})
+		db.Create(&domain.WorkStats{WorkID: targetWork.ID, Views: 20, Likes: 10})
 
-	assert.Len(t, finalTargetWork.Authors, 2, "Authors should be merged")
-	assert.Len(t, finalTargetWork.Tags, 2, "Tags should be merged")
+		// --- Execute Merge ---
+		ctx := context.WithValue(context.Background(), platform_auth.ClaimsContextKey, &platform_auth.Claims{UserID: 1, Role: string(domain.UserRoleAdmin)})
+		err = commands.MergeWork(ctx, sourceWork.ID, targetWork.ID)
+		assert.NoError(t, err)
 
-	// 3. Stats should be merged
-	var finalStats domain.WorkStats
-	db.Where("work_id = ?", targetWork.ID).First(&finalStats)
-	assert.Equal(t, int64(30), finalStats.Views, "Views should be summed")
-	assert.Equal(t, int64(15), finalStats.Likes, "Likes should be summed")
+		// --- Assertions ---
+		// 1. Source work should be deleted
+		var deletedWork domain.Work
+		err = db.First(&deletedWork, sourceWork.ID).Error
+		assert.Error(t, err)
+		assert.True(t, errors.Is(err, gorm.ErrRecordNotFound))
 
-	// 4. Source stats should be deleted
-	var deletedStats domain.WorkStats
-	err = db.First(&deletedStats, "work_id = ?", sourceWork.ID).Error
-	assert.Error(t, err, "Source stats should be deleted")
-	assert.True(t, errors.Is(err, gorm.ErrRecordNotFound))
+		// 2. Target work should have merged data
+		var finalTargetWork domain.Work
+		db.Preload("Translations").Preload("Authors").Preload("Tags").First(&finalTargetWork, targetWork.ID)
+
+		assert.Len(t, finalTargetWork.Translations, 2, "Should have two translations after merge")
+		foundEn := false
+		foundFr := false
+		for _, tr := range finalTargetWork.Translations {
+			if tr.Language == "en" {
+				foundEn = true
+				assert.Equal(t, "Target English", tr.Title, "Should keep target's English translation")
+			}
+			if tr.Language == "fr" {
+				foundFr = true
+				assert.Equal(t, "Source French", tr.Title, "Should merge source's French translation")
+			}
+		}
+		assert.True(t, foundEn, "English translation should be present")
+		assert.True(t, foundFr, "French translation should be present")
+
+		assert.Len(t, finalTargetWork.Authors, 2, "Authors should be merged")
+		assert.Len(t, finalTargetWork.Tags, 2, "Tags should be merged")
+
+		// 3. Stats should be merged
+		var finalStats domain.WorkStats
+		db.Where("work_id = ?", targetWork.ID).First(&finalStats)
+		assert.Equal(t, int64(30), finalStats.Views, "Views should be summed")
+		assert.Equal(t, int64(15), finalStats.Likes, "Likes should be summed")
+
+		// 4. Source stats should be deleted
+		var deletedStats domain.WorkStats
+		err = db.First(&deletedStats, "work_id = ?", sourceWork.ID).Error
+		assert.Error(t, err, "Source stats should be deleted")
+		assert.True(t, errors.Is(err, gorm.ErrRecordNotFound))
+	})
+
+	t.Run("Success with no target stats", func(t *testing.T) {
+		sourceWork := &domain.Work{Title: "Source with Stats"}
+		db.Create(sourceWork)
+		db.Create(&domain.WorkStats{WorkID: sourceWork.ID, Views: 15, Likes: 7})
+
+		targetWork := &domain.Work{Title: "Target without Stats"}
+		db.Create(targetWork)
+
+		ctx := context.WithValue(context.Background(), platform_auth.ClaimsContextKey, &platform_auth.Claims{UserID: 1, Role: string(domain.UserRoleAdmin)})
+		err := commands.MergeWork(ctx, sourceWork.ID, targetWork.ID)
+		assert.NoError(t, err)
+
+		var finalStats domain.WorkStats
+		db.Where("work_id = ?", targetWork.ID).First(&finalStats)
+		assert.Equal(t, int64(15), finalStats.Views)
+		assert.Equal(t, int64(7), finalStats.Likes)
+	})
+
+	t.Run("Forbidden for non-admin", func(t *testing.T) {
+		sourceWork := &domain.Work{Title: "Forbidden Source"}
+		db.Create(sourceWork)
+		targetWork := &domain.Work{Title: "Forbidden Target"}
+		db.Create(targetWork)
+
+		ctx := context.WithValue(context.Background(), platform_auth.ClaimsContextKey, &platform_auth.Claims{UserID: 2, Role: string(domain.UserRoleReader)})
+		err := commands.MergeWork(ctx, sourceWork.ID, targetWork.ID)
+
+		assert.Error(t, err)
+		assert.True(t, errors.Is(err, domain.ErrForbidden))
+	})
+
+	t.Run("Source work not found", func(t *testing.T) {
+		targetWork := &domain.Work{Title: "Existing Target"}
+		db.Create(targetWork)
+		ctx := context.WithValue(context.Background(), platform_auth.ClaimsContextKey, &platform_auth.Claims{UserID: 1, Role: string(domain.UserRoleAdmin)})
+
+		err := commands.MergeWork(ctx, 99999, targetWork.ID)
+
+		assert.Error(t, err)
+		assert.Contains(t, err.Error(), "entity not found")
+	})
+
+	t.Run("Target work not found", func(t *testing.T) {
+		sourceWork := &domain.Work{Title: "Existing Source"}
+		db.Create(sourceWork)
+		ctx := context.WithValue(context.Background(), platform_auth.ClaimsContextKey, &platform_auth.Claims{UserID: 1, Role: string(domain.UserRoleAdmin)})
+
+		err := commands.MergeWork(ctx, sourceWork.ID, 99999)
+
+		assert.Error(t, err)
+		assert.Contains(t, err.Error(), "entity not found")
+	})
+
+	t.Run("Cannot merge work into itself", func(t *testing.T) {
+		work := &domain.Work{Title: "Self Merge Work"}
+		db.Create(work)
+		ctx := context.WithValue(context.Background(), platform_auth.ClaimsContextKey, &platform_auth.Claims{UserID: 1, Role: string(domain.UserRoleAdmin)})
+
+		err := commands.MergeWork(ctx, work.ID, work.ID)
+
+		assert.Error(t, err)
+		assert.Contains(t, err.Error(), "source and target work IDs cannot be the same")
+	})
 }
\ No newline at end of file
diff --git a/internal/app/work/main_test.go b/internal/app/work/main_test.go
index 02b034e..1d02791 100644
--- a/internal/app/work/main_test.go
+++ b/internal/app/work/main_test.go
@@ -18,6 +18,7 @@ type mockWorkRepository struct {
 	findByCategoryFunc      func(ctx context.Context, categoryID uint) ([]domain.Work, error)
 	findByLanguageFunc      func(ctx context.Context, language string, page, pageSize int) (*domain.PaginatedResult[domain.Work], error)
 	isAuthorFunc            func(ctx context.Context, workID uint, authorID uint) (bool, error)
+	listByCollectionIDFunc  func(ctx context.Context, collectionID uint) ([]domain.Work, error)
 }
 
 func (m *mockWorkRepository) IsAuthor(ctx context.Context, workID uint, authorID uint) (bool, error) {
@@ -57,6 +58,13 @@ func (m *mockWorkRepository) List(ctx context.Context, page, pageSize int) (*dom
 	}
 	return nil, nil
 }
+
+func (m *mockWorkRepository) ListByCollectionID(ctx context.Context, collectionID uint) ([]domain.Work, error) {
+	if m.listByCollectionIDFunc != nil {
+		return m.listByCollectionIDFunc(ctx, collectionID)
+	}
+	return nil, nil
+}
 func (m *mockWorkRepository) GetWithTranslations(ctx context.Context, id uint) (*domain.Work, error) {
 	if m.getWithTranslationsFunc != nil {
 		return m.getWithTranslationsFunc(ctx, id)
diff --git a/internal/app/work/mock_analytics_service_test.go b/internal/app/work/mock_analytics_service_test.go
index 559111e..363a346 100644
--- a/internal/app/work/mock_analytics_service_test.go
+++ b/internal/app/work/mock_analytics_service_test.go
@@ -11,6 +11,15 @@ type mockAnalyticsService struct {
 	updateWorkSentimentFunc        func(ctx context.Context, workID uint) error
 	updateTranslationReadingTimeFunc func(ctx context.Context, translationID uint) error
 	updateTranslationSentimentFunc   func(ctx context.Context, translationID uint) error
+	getOrCreateWorkStatsFunc       func(ctx context.Context, workID uint) (*domain.WorkStats, error)
+	updateWorkStatsFunc            func(ctx context.Context, workID uint, stats domain.WorkStats) error
+}
+
+func (m *mockAnalyticsService) UpdateWorkStats(ctx context.Context, workID uint, stats domain.WorkStats) error {
+	if m.updateWorkStatsFunc != nil {
+		return m.updateWorkStatsFunc(ctx, workID, stats)
+	}
+	return nil
 }
 
 func (m *mockAnalyticsService) UpdateWorkReadingTime(ctx context.Context, workID uint) error {
@@ -78,6 +87,9 @@ func (m *mockAnalyticsService) IncrementTranslationShares(ctx context.Context, t
 	return nil
 }
 func (m *mockAnalyticsService) GetOrCreateWorkStats(ctx context.Context, workID uint) (*domain.WorkStats, error) {
+	if m.getOrCreateWorkStatsFunc != nil {
+		return m.getOrCreateWorkStatsFunc(ctx, workID)
+	}
 	return nil, nil
 }
 func (m *mockAnalyticsService) GetOrCreateTranslationStats(ctx context.Context, translationID uint) (*domain.TranslationStats, error) {
diff --git a/internal/app/work/queries_test.go b/internal/app/work/queries_test.go
index 5817edc..5ca36d9 100644
--- a/internal/app/work/queries_test.go
+++ b/internal/app/work/queries_test.go
@@ -45,6 +45,22 @@ func (s *WorkQueriesSuite) TestGetWorkByID_ZeroID() {
 	assert.Nil(s.T(), w)
 }
 
+func (s *WorkQueriesSuite) TestListByCollectionID_Success() {
+	works := []domain.Work{{Title: "Test Work"}}
+	s.repo.listByCollectionIDFunc = func(ctx context.Context, collectionID uint) ([]domain.Work, error) {
+		return works, nil
+	}
+	w, err := s.queries.ListByCollectionID(context.Background(), 1)
+	assert.NoError(s.T(), err)
+	assert.Equal(s.T(), works, w)
+}
+
+func (s *WorkQueriesSuite) TestListByCollectionID_ZeroID() {
+	w, err := s.queries.ListByCollectionID(context.Background(), 0)
+	assert.Error(s.T(), err)
+	assert.Nil(s.T(), w)
+}
+
 func (s *WorkQueriesSuite) TestListWorks_Success() {
 	domainWorks := &domain.PaginatedResult[domain.Work]{
 		Items: []domain.Work{
diff --git a/internal/app/work/service_test.go b/internal/app/work/service_test.go
new file mode 100644
index 0000000..a7a881f
--- /dev/null
+++ b/internal/app/work/service_test.go
@@ -0,0 +1,24 @@
+package work
+
+import (
+	"testing"
+	"tercul/internal/app/authz"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewService(t *testing.T) {
+	// Arrange
+	mockRepo := &mockWorkRepository{}
+	mockSearchClient := &mockSearchClient{}
+	mockAuthzSvc := &authz.Service{}
+	mockAnalyticsSvc := &mockAnalyticsService{}
+
+	// Act
+	service := NewService(mockRepo, mockSearchClient, mockAuthzSvc, mockAnalyticsSvc)
+
+	// Assert
+	assert.NotNil(t, service, "The new service should not be nil")
+	assert.NotNil(t, service.Commands, "The service Commands should not be nil")
+	assert.NotNil(t, service.Queries, "The service Queries should not be nil")
+}
\ No newline at end of file
diff --git a/internal/data/sql/analytics_repository_test.go b/internal/data/sql/analytics_repository_test.go
new file mode 100644
index 0000000..9101cd5
--- /dev/null
+++ b/internal/data/sql/analytics_repository_test.go
@@ -0,0 +1,204 @@
+package sql_test
+
+import (
+	"context"
+	"testing"
+	"tercul/internal/app/analytics"
+	"tercul/internal/data/sql"
+	"tercul/internal/domain"
+	"tercul/internal/platform/config"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+)
+
+// newTestAnalyticsRepoWithSQLite sets up an in-memory SQLite database for testing.
+func newTestAnalyticsRepoWithSQLite(t *testing.T) (analytics.Repository, *gorm.DB) {
+	// Using "file::memory:?cache=shared" to ensure the in-memory database is shared across connections in the same process.
+	db, err := gorm.Open(sqlite.Open("file::memory:?cache=shared"), &gorm.Config{})
+	require.NoError(t, err)
+
+	// Auto-migrate the necessary schemas
+	err = db.AutoMigrate(
+		&domain.Work{},
+		&domain.WorkStats{},
+		&domain.Translation{},
+		&domain.TranslationStats{},
+		&domain.Trending{},
+		&domain.UserEngagement{},
+		&domain.User{},
+	)
+	require.NoError(t, err)
+
+	cfg := &config.Config{}
+	repo := sql.NewAnalyticsRepository(db, cfg)
+
+	// Clean up the database after the test
+	t.Cleanup(func() {
+		sqlDB, err := db.DB()
+		require.NoError(t, err)
+		err = sqlDB.Close()
+		require.NoError(t, err)
+	})
+
+	return repo, db
+}
+
+func TestAnalyticsRepository_IncrementWorkCounter(t *testing.T) {
+	repo, db := newTestAnalyticsRepoWithSQLite(t)
+	ctx := context.Background()
+
+	// Setup: Create a work to associate stats with
+	work := domain.Work{Title: "Test Work"}
+	require.NoError(t, db.Create(&work).Error)
+
+	t.Run("creates_new_stats_if_not_exist", func(t *testing.T) {
+		err := repo.IncrementWorkCounter(ctx, work.ID, "views", 5)
+		require.NoError(t, err)
+
+		var stats domain.WorkStats
+		err = db.Where("work_id = ?", work.ID).First(&stats).Error
+		require.NoError(t, err)
+		assert.Equal(t, int64(5), stats.Views)
+	})
+
+	t.Run("increments_existing_stats", func(t *testing.T) {
+		// Increment again
+		err := repo.IncrementWorkCounter(ctx, work.ID, "views", 3)
+		require.NoError(t, err)
+
+		var stats domain.WorkStats
+		err = db.Where("work_id = ?", work.ID).First(&stats).Error
+		require.NoError(t, err)
+		assert.Equal(t, int64(8), stats.Views) // 5 + 3
+	})
+
+	t.Run("invalid_field", func(t *testing.T) {
+		err := repo.IncrementWorkCounter(ctx, work.ID, "invalid_field", 1)
+		assert.Error(t, err)
+	})
+}
+
+func TestAnalyticsRepository_GetTrendingWorks(t *testing.T) {
+	repo, db := newTestAnalyticsRepoWithSQLite(t)
+	ctx := context.Background()
+
+	// Setup: Create some works and trending data
+	work1 := domain.Work{Title: "Trending Work 1"}
+	work2 := domain.Work{Title: "Trending Work 2"}
+	require.NoError(t, db.Create(&work1).Error)
+	require.NoError(t, db.Create(&work2).Error)
+
+	trendingData := []*domain.Trending{
+		{EntityID: work1.ID, EntityType: "Work", Rank: 1, TimePeriod: "daily"},
+		{EntityID: work2.ID, EntityType: "Work", Rank: 2, TimePeriod: "daily"},
+	}
+	require.NoError(t, db.Create(&trendingData).Error)
+
+	t.Run("success", func(t *testing.T) {
+		works, err := repo.GetTrendingWorks(ctx, "daily", 5)
+		require.NoError(t, err)
+		require.Len(t, works, 2)
+		assert.Equal(t, work1.ID, works[0].ID)
+		assert.Equal(t, work2.ID, works[1].ID)
+	})
+}
+
+func TestAnalyticsRepository_UpdateTrendingWorks(t *testing.T) {
+	repo, db := newTestAnalyticsRepoWithSQLite(t)
+	ctx := context.Background()
+
+	// Setup: Create an old trending record
+	oldTrending := domain.Trending{EntityID: 99, EntityType: "Work", Rank: 1, TimePeriod: "daily"}
+	require.NoError(t, db.Create(&oldTrending).Error)
+
+	newTrendingData := []*domain.Trending{
+		{EntityID: 1, EntityType: "Work", Rank: 1, Score: 100, TimePeriod: "daily"},
+		{EntityID: 2, EntityType: "Work", Rank: 2, Score: 90, TimePeriod: "daily"},
+	}
+
+	err := repo.UpdateTrendingWorks(ctx, "daily", newTrendingData)
+	require.NoError(t, err)
+
+	var trendingResult []domain.Trending
+	db.Where("time_period = ?", "daily").Order("rank asc").Find(&trendingResult)
+
+	require.Len(t, trendingResult, 2)
+	assert.Equal(t, uint(1), trendingResult[0].EntityID)
+	assert.Equal(t, uint(2), trendingResult[1].EntityID)
+}
+
+func TestAnalyticsRepository_GetOrCreate(t *testing.T) {
+	repo, db := newTestAnalyticsRepoWithSQLite(t)
+	ctx := context.Background()
+
+	work := domain.Work{Title: "Test Work"}
+	require.NoError(t, db.Create(&work).Error)
+	translation := domain.Translation{Title: "Test Translation", TranslatableID: work.ID, TranslatableType: "Work"}
+	require.NoError(t, db.Create(&translation).Error)
+	user := domain.User{Username: "testuser", Email: "test@test.com"}
+	require.NoError(t, db.Create(&user).Error)
+
+	t.Run("GetOrCreateWorkStats", func(t *testing.T) {
+		// Create
+		stats, err := repo.GetOrCreateWorkStats(ctx, work.ID)
+		require.NoError(t, err)
+		assert.Equal(t, work.ID, stats.WorkID)
+
+		// Get
+		stats2, err := repo.GetOrCreateWorkStats(ctx, work.ID)
+		require.NoError(t, err)
+		assert.Equal(t, stats.ID, stats2.ID)
+	})
+
+	t.Run("GetOrCreateTranslationStats", func(t *testing.T) {
+		// Create
+		stats, err := repo.GetOrCreateTranslationStats(ctx, translation.ID)
+		require.NoError(t, err)
+		assert.Equal(t, translation.ID, stats.TranslationID)
+
+		// Get
+		stats2, err := repo.GetOrCreateTranslationStats(ctx, translation.ID)
+		require.NoError(t, err)
+		assert.Equal(t, stats.ID, stats2.ID)
+	})
+
+	t.Run("GetOrCreateUserEngagement", func(t *testing.T) {
+		date := time.Now().Truncate(24 * time.Hour)
+		// Create
+		eng, err := repo.GetOrCreateUserEngagement(ctx, user.ID, date)
+		require.NoError(t, err)
+		assert.Equal(t, user.ID, eng.UserID)
+
+		// Get
+		eng2, err := repo.GetOrCreateUserEngagement(ctx, user.ID, date)
+		require.NoError(t, err)
+		assert.Equal(t, eng.ID, eng2.ID)
+	})
+}
+
+func TestAnalyticsRepository_UpdateUserEngagement(t *testing.T) {
+	repo, db := newTestAnalyticsRepoWithSQLite(t)
+	ctx := context.Background()
+
+	user := domain.User{Username: "testuser", Email: "test@test.com"}
+	require.NoError(t, db.Create(&user).Error)
+	date := time.Now().Truncate(24 * time.Hour)
+	engagement, err := repo.GetOrCreateUserEngagement(ctx, user.ID, date)
+	require.NoError(t, err)
+
+	engagement.LikesGiven = 15
+	engagement.WorksRead = 10
+
+	err = repo.UpdateUserEngagement(ctx, engagement)
+	require.NoError(t, err)
+
+	var updatedEngagement domain.UserEngagement
+	db.First(&updatedEngagement, engagement.ID)
+
+	assert.Equal(t, 15, updatedEngagement.LikesGiven)
+	assert.Equal(t, 10, updatedEngagement.WorksRead)
+}
\ No newline at end of file
diff --git a/internal/data/sql/auth_repository_test.go b/internal/data/sql/auth_repository_test.go
new file mode 100644
index 0000000..4a4da96
--- /dev/null
+++ b/internal/data/sql/auth_repository_test.go
@@ -0,0 +1,91 @@
+package sql_test
+
+import (
+	"context"
+	"testing"
+	"tercul/internal/data/sql"
+	"tercul/internal/domain"
+	"tercul/internal/platform/config"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+)
+
+// newTestAuthRepoWithSQLite sets up an in-memory SQLite database for auth repository testing.
+func newTestAuthRepoWithSQLite(t *testing.T) (domain.AuthRepository, *gorm.DB) {
+	db, err := gorm.Open(sqlite.Open("file::memory:?cache=shared"), &gorm.Config{})
+	require.NoError(t, err)
+
+	// Auto-migrate the necessary schemas
+	err = db.AutoMigrate(
+		&domain.User{},
+		&domain.UserSession{},
+	)
+	require.NoError(t, err)
+
+	cfg := &config.Config{}
+	repo := sql.NewAuthRepository(db, cfg)
+
+	// Clean up the database after the test
+	t.Cleanup(func() {
+		sqlDB, err := db.DB()
+		require.NoError(t, err)
+		err = sqlDB.Close()
+		require.NoError(t, err)
+	})
+
+	return repo, db
+}
+
+func TestAuthRepository_StoreToken(t *testing.T) {
+	repo, db := newTestAuthRepoWithSQLite(t)
+	ctx := context.Background()
+
+	// Setup: Create a user
+	user := domain.User{Username: "authuser", Email: "auth@test.com"}
+	require.NoError(t, db.Create(&user).Error)
+
+	token := "my-secret-token"
+	expiresAt := time.Now().Add(1 * time.Hour)
+
+	err := repo.StoreToken(ctx, user.ID, token, expiresAt)
+	require.NoError(t, err)
+
+	var session domain.UserSession
+	err = db.Where("token = ?", token).First(&session).Error
+	require.NoError(t, err)
+
+	assert.Equal(t, user.ID, session.UserID)
+	assert.Equal(t, token, session.Token)
+	// Truncate to a reasonable precision for comparison
+	assert.WithinDuration(t, expiresAt, session.ExpiresAt, time.Second)
+}
+
+func TestAuthRepository_DeleteToken(t *testing.T) {
+	repo, db := newTestAuthRepoWithSQLite(t)
+	ctx := context.Background()
+
+	// Setup: Create a user and a session
+	user := domain.User{Username: "authuser2", Email: "auth2@test.com"}
+	require.NoError(t, db.Create(&user).Error)
+	token := "token-to-delete"
+	session := &domain.UserSession{
+		UserID:    user.ID,
+		Token:     token,
+		ExpiresAt: time.Now().Add(1 * time.Hour),
+	}
+	require.NoError(t, db.Create(session).Error)
+
+	// Delete the token
+	err := repo.DeleteToken(ctx, token)
+	require.NoError(t, err)
+
+	// Verify it's gone
+	var deletedSession domain.UserSession
+	err = db.Where("token = ?", token).First(&deletedSession).Error
+	assert.Error(t, err)
+	assert.Equal(t, gorm.ErrRecordNotFound, err)
+}
\ No newline at end of file
diff --git a/internal/data/sql/copyright_claim_repository_test.go b/internal/data/sql/copyright_claim_repository_test.go
new file mode 100644
index 0000000..2f31aa7
--- /dev/null
+++ b/internal/data/sql/copyright_claim_repository_test.go
@@ -0,0 +1,122 @@
+package sql_test
+
+import (
+	"context"
+	"testing"
+	"tercul/internal/data/sql"
+	"tercul/internal/domain"
+	"tercul/internal/platform/config"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+)
+
+// newTestCopyrightClaimRepoWithSQLite sets up an in-memory SQLite database for copyright claim repository testing.
+func newTestCopyrightClaimRepoWithSQLite(t *testing.T) (domain.CopyrightClaimRepository, *gorm.DB) {
+	db, err := gorm.Open(sqlite.Open("file::memory:?cache=shared"), &gorm.Config{})
+	require.NoError(t, err)
+
+	// Auto-migrate the necessary schemas
+	err = db.AutoMigrate(
+		&domain.User{},
+		&domain.Work{},
+		&domain.CopyrightClaim{},
+	)
+	require.NoError(t, err)
+
+	cfg := &config.Config{}
+	repo := sql.NewCopyrightClaimRepository(db, cfg)
+
+	// Clean up the database after the test
+	t.Cleanup(func() {
+		sqlDB, err := db.DB()
+		require.NoError(t, err)
+		err = sqlDB.Close()
+		require.NoError(t, err)
+	})
+
+	return repo, db
+}
+
+func TestCopyrightClaimRepository_ListByWorkID(t *testing.T) {
+	repo, db := newTestCopyrightClaimRepoWithSQLite(t)
+	ctx := context.Background()
+
+	// Setup: Create a user and a work
+	user := domain.User{Username: "claimuser", Email: "claim@test.com"}
+	require.NoError(t, db.Create(&user).Error)
+	work1 := domain.Work{Title: "Work 1"}
+	require.NoError(t, db.Create(&work1).Error)
+	work2 := domain.Work{Title: "Work 2"}
+	require.NoError(t, db.Create(&work2).Error)
+
+	// Create some claims
+	claim1 := domain.CopyrightClaim{UserID: &user.ID, WorkID: &work1.ID, Details: "Claim 1", ClaimDate: time.Now()}
+	claim2 := domain.CopyrightClaim{UserID: &user.ID, WorkID: &work1.ID, Details: "Claim 2", ClaimDate: time.Now()}
+	claim3 := domain.CopyrightClaim{UserID: &user.ID, WorkID: &work2.ID, Details: "Claim 3", ClaimDate: time.Now()}
+	require.NoError(t, db.Create(&claim1).Error)
+	require.NoError(t, db.Create(&claim2).Error)
+	require.NoError(t, db.Create(&claim3).Error)
+
+	t.Run("finds_claims_for_work1", func(t *testing.T) {
+		claims, err := repo.ListByWorkID(ctx, work1.ID)
+		require.NoError(t, err)
+		assert.Len(t, claims, 2)
+	})
+
+	t.Run("finds_claims_for_work2", func(t *testing.T) {
+		claims, err := repo.ListByWorkID(ctx, work2.ID)
+		require.NoError(t, err)
+		assert.Len(t, claims, 1)
+		assert.Equal(t, "Claim 3", claims[0].Details)
+	})
+
+	t.Run("returns_empty_slice_for_no_claims", func(t *testing.T) {
+		claims, err := repo.ListByWorkID(ctx, 999) // Non-existent work
+		require.NoError(t, err)
+		assert.Empty(t, claims)
+	})
+}
+
+func TestCopyrightClaimRepository_ListByUserID(t *testing.T) {
+	repo, db := newTestCopyrightClaimRepoWithSQLite(t)
+	ctx := context.Background()
+
+	// Setup: Create users and a work
+	user1 := domain.User{Username: "user1", Email: "user1@test.com"}
+	require.NoError(t, db.Create(&user1).Error)
+	user2 := domain.User{Username: "user2", Email: "user2@test.com"}
+	require.NoError(t, db.Create(&user2).Error)
+	work := domain.Work{Title: "Test Work"}
+	require.NoError(t, db.Create(&work).Error)
+
+	// Create some claims
+	claim1 := domain.CopyrightClaim{UserID: &user1.ID, WorkID: &work.ID, Details: "Claim 1", ClaimDate: time.Now()}
+	claim2 := domain.CopyrightClaim{UserID: &user2.ID, WorkID: &work.ID, Details: "Claim 2", ClaimDate: time.Now()}
+	claim3 := domain.CopyrightClaim{UserID: &user2.ID, WorkID: &work.ID, Details: "Claim 3", ClaimDate: time.Now()}
+	require.NoError(t, db.Create(&claim1).Error)
+	require.NoError(t, db.Create(&claim2).Error)
+	require.NoError(t, db.Create(&claim3).Error)
+
+	t.Run("finds_claims_for_user1", func(t *testing.T) {
+		claims, err := repo.ListByUserID(ctx, user1.ID)
+		require.NoError(t, err)
+		assert.Len(t, claims, 1)
+		assert.Equal(t, "Claim 1", claims[0].Details)
+	})
+
+	t.Run("finds_claims_for_user2", func(t *testing.T) {
+		claims, err := repo.ListByUserID(ctx, user2.ID)
+		require.NoError(t, err)
+		assert.Len(t, claims, 2)
+	})
+
+	t.Run("returns_empty_slice_for_no_claims", func(t *testing.T) {
+		claims, err := repo.ListByUserID(ctx, 999) // Non-existent user
+		require.NoError(t, err)
+		assert.Empty(t, claims)
+	})
+}
\ No newline at end of file
diff --git a/internal/data/sql/copyright_repository_test.go b/internal/data/sql/copyright_repository_test.go
index 78468b7..d44474e 100644
--- a/internal/data/sql/copyright_repository_test.go
+++ b/internal/data/sql/copyright_repository_test.go
@@ -127,7 +127,7 @@ func (s *CopyrightRepositoryTestSuite) TestGetTranslationByLanguage() {
 
 		_, err := s.repo.GetTranslationByLanguage(context.Background(), copyrightID, languageCode)
 		s.Require().Error(err)
-		s.Require().Equal(sql.ErrEntityNotFound, err)
+		s.Require().Contains(err.Error(), "entity not found")
 	})
 }
 
diff --git a/internal/domain/entities.go b/internal/domain/entities.go
index f59d1e9..792bbaf 100644
--- a/internal/domain/entities.go
+++ b/internal/domain/entities.go
@@ -581,8 +581,10 @@ type CopyrightClaim struct {
 	ClaimDate time.Time            `gorm:"not null"`
 	Resolution string               `gorm:"type:text"`
 	ResolvedAt *time.Time
-	UserID    *uint
-	User      *User `gorm:"foreignKey:UserID"`
+	UserID     *uint
+	User       *User `gorm:"foreignKey:UserID"`
+	WorkID     *uint
+	Work       *Work `gorm:"foreignKey:WorkID"`
 }
 type MonetizationType string
 const (
diff --git a/internal/platform/cache/redis_cache_test.go b/internal/platform/cache/redis_cache_test.go
new file mode 100644
index 0000000..43e179a
--- /dev/null
+++ b/internal/platform/cache/redis_cache_test.go
@@ -0,0 +1,409 @@
+package cache_test
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"testing"
+	"tercul/internal/platform/cache"
+	"tercul/internal/platform/config"
+	"time"
+
+	"github.com/go-redis/redismock/v9"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewRedisCache(t *testing.T) {
+	client, _ := redismock.NewClientMock()
+	keyGen := cache.NewDefaultKeyGenerator("test:")
+	defaultExpiry := 2 * time.Hour
+
+	c := cache.NewRedisCache(client, keyGen, defaultExpiry)
+	require.NotNil(t, c)
+}
+
+func TestNewDefaultRedisCache(t *testing.T) {
+	t.Run("success", func(t *testing.T) {
+		// This test requires a running Redis instance or a mock for the Ping command.
+		// For now, we'll just test that the function returns a non-nil cache
+		// when the config is valid. A more comprehensive test would involve
+		// mocking the redis.NewClient and its Ping method.
+		cfg := &config.Config{
+			RedisAddr: "localhost:6379",
+		}
+		// Since this function actually tries to connect, we can't fully test it in a unit test
+		// without a live redis. We will skip a full test here and focus on the other methods.
+		// In a real-world scenario, we might use a test container with Redis.
+		// For now, we'll just ensure it doesn't panic with a basic config.
+		// A proper integration test would be better suited for this.
+		_ = cfg
+		// _, err := cache.NewDefaultRedisCache(cfg)
+		// assert.NoError(t, err)
+	})
+
+	t.Run("connection error", func(t *testing.T) {
+		cfg := &config.Config{
+			RedisAddr: "localhost:9999", // Invalid address
+		}
+		_, err := cache.NewDefaultRedisCache(cfg)
+		assert.Error(t, err)
+	})
+}
+
+func TestRedisCache_Get(t *testing.T) {
+	client, mock := redismock.NewClientMock()
+	c := cache.NewRedisCache(client, nil, time.Hour)
+	ctx := context.Background()
+	key := "test-key"
+	expectedValue := map[string]string{"foo": "bar"}
+	expectedBytes, _ := json.Marshal(expectedValue)
+
+	t.Run("success", func(t *testing.T) {
+		mock.ExpectGet(key).SetVal(string(expectedBytes))
+
+		var result map[string]string
+		err := c.Get(ctx, key, &result)
+
+		assert.NoError(t, err)
+		assert.Equal(t, expectedValue, result)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("cache miss", func(t *testing.T) {
+		mock.ExpectGet(key).RedisNil()
+
+		var result map[string]string
+		err := c.Get(ctx, key, &result)
+
+		assert.Error(t, err)
+		assert.Equal(t, "cache miss", err.Error())
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("redis error", func(t *testing.T) {
+		mock.ExpectGet(key).SetErr(errors.New("redis error"))
+
+		var result map[string]string
+		err := c.Get(ctx, key, &result)
+
+		assert.Error(t, err)
+		assert.Equal(t, "redis error", err.Error())
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+}
+
+func TestRedisCache_InvalidateEntityType(t *testing.T) {
+	ctx := context.Background()
+	entityType := "user"
+	pattern := "tercul:user:*"
+
+	t.Run("success with multiple batches", func(t *testing.T) {
+		client, mock := redismock.NewClientMock()
+		keyGen := cache.NewDefaultKeyGenerator("tercul:")
+		c := cache.NewRedisCache(client, keyGen, time.Hour)
+
+		keysBatch1 := make([]string, 100)
+		for i := 0; i < 100; i++ {
+			keysBatch1[i] = fmt.Sprintf("tercul:user:key%d", i)
+		}
+		keysBatch2 := []string{"tercul:user:key101", "tercul:user:key102"}
+
+		// Mocking the SCAN and DEL calls in the correct order
+		mock.ExpectScan(0, pattern, 100).SetVal(keysBatch1, 1)
+		mock.ExpectDel(keysBatch1...).SetVal(100)
+		mock.ExpectScan(1, pattern, 100).SetVal(keysBatch2, 0)
+		mock.ExpectDel(keysBatch2...).SetVal(2)
+
+		err := c.InvalidateEntityType(ctx, entityType)
+		assert.NoError(t, err)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("success with single batch", func(t *testing.T) {
+		client, mock := redismock.NewClientMock()
+		keyGen := cache.NewDefaultKeyGenerator("tercul:")
+		c := cache.NewRedisCache(client, keyGen, time.Hour)
+
+		keys := []string{"tercul:user:key1", "tercul:user:key2"}
+		mock.ExpectScan(0, pattern, 100).SetVal(keys, 0)
+		mock.ExpectDel(keys...).SetVal(2)
+
+		err := c.InvalidateEntityType(ctx, entityType)
+		assert.NoError(t, err)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("scan error", func(t *testing.T) {
+		client, mock := redismock.NewClientMock()
+		keyGen := cache.NewDefaultKeyGenerator("tercul:")
+		c := cache.NewRedisCache(client, keyGen, time.Hour)
+
+		mock.ExpectScan(0, pattern, 100).SetErr(errors.New("scan error"))
+
+		err := c.InvalidateEntityType(ctx, entityType)
+		assert.Error(t, err)
+		assert.Equal(t, "scan error", err.Error())
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("del error", func(t *testing.T) {
+		client, mock := redismock.NewClientMock()
+		keyGen := cache.NewDefaultKeyGenerator("tercul:")
+		c := cache.NewRedisCache(client, keyGen, time.Hour)
+
+		keys := []string{"tercul:user:key1"}
+		mock.ExpectScan(0, pattern, 100).SetVal(keys, 0)
+		mock.ExpectDel(keys...).SetErr(errors.New("del error"))
+
+		err := c.InvalidateEntityType(ctx, entityType)
+		assert.Error(t, err)
+		assert.Equal(t, "del error", err.Error())
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+}
+
+func TestRedisCache_GetMulti(t *testing.T) {
+	client, mock := redismock.NewClientMock()
+	c := cache.NewRedisCache(client, nil, time.Hour)
+	ctx := context.Background()
+	keys := []string{"key1", "key2", "key3"}
+	expectedValues := []interface{}{"value1", nil, "value3"}
+	expectedResult := map[string][]byte{
+		"key1": []byte("value1"),
+		"key3": []byte("value3"),
+	}
+
+	t.Run("success", func(t *testing.T) {
+		mock.ExpectMGet(keys...).SetVal(expectedValues)
+
+		result, err := c.GetMulti(ctx, keys)
+
+		assert.NoError(t, err)
+		assert.Equal(t, expectedResult, result)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("no keys", func(t *testing.T) {
+		result, err := c.GetMulti(ctx, []string{})
+		assert.NoError(t, err)
+		assert.Empty(t, result)
+	})
+
+	t.Run("redis error", func(t *testing.T) {
+		mock.ExpectMGet(keys...).SetErr(errors.New("redis error"))
+
+		_, err := c.GetMulti(ctx, keys)
+
+		assert.Error(t, err)
+		assert.Equal(t, "redis error", err.Error())
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+}
+
+func TestRedisCache_SetMulti(t *testing.T) {
+	ctx := context.Background()
+	items := map[string]interface{}{
+		"key1": "value1",
+		"key2": 123,
+	}
+
+	t.Run("success", func(t *testing.T) {
+		client, mock := redismock.NewClientMock()
+		c := cache.NewRedisCache(client, nil, time.Hour)
+		mock.MatchExpectationsInOrder(false)
+
+		// Expect each Set command within the pipeline
+		for key, value := range items {
+			data, _ := json.Marshal(value)
+			mock.ExpectSet(key, data, time.Hour).SetVal("OK")
+		}
+
+		// The SetMulti function will call Exec(), which triggers the mock's pipeline hook
+		err := c.SetMulti(ctx, items, 0)
+
+		assert.NoError(t, err)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("no items", func(t *testing.T) {
+		client, _ := redismock.NewClientMock()
+		c := cache.NewRedisCache(client, nil, time.Hour)
+		err := c.SetMulti(ctx, map[string]interface{}{}, 0)
+		assert.NoError(t, err)
+	})
+
+	t.Run("redis error", func(t *testing.T) {
+		client, mock := redismock.NewClientMock()
+		c := cache.NewRedisCache(client, nil, time.Hour)
+		mock.MatchExpectationsInOrder(false)
+
+		// To simulate a pipeline execution error, we make one of the inner commands fail.
+		// The hook will stop processing on the first error and return it.
+		data1, _ := json.Marshal("value1")
+		mock.ExpectSet("key1", data1, time.Hour).SetErr(errors.New("redis error"))
+
+		data2, _ := json.Marshal(123)
+		mock.ExpectSet("key2", data2, time.Hour).SetVal("OK")
+
+		err := c.SetMulti(ctx, items, 0)
+
+		assert.Error(t, err)
+		assert.Contains(t, err.Error(), "redis error")
+	})
+}
+
+func TestRedisCache_EntityOperations(t *testing.T) {
+	client, mock := redismock.NewClientMock()
+	keyGen := cache.NewDefaultKeyGenerator("tercul:")
+	c := cache.NewRedisCache(client, keyGen, time.Hour)
+	ctx := context.Background()
+
+	entityType := "user"
+	id := uint(123)
+	entityKey := "tercul:user:id:123"
+	value := map[string]string{"name": "test"}
+	valueBytes, _ := json.Marshal(value)
+
+	page := 1
+	pageSize := 10
+	listKey := "tercul:user:list:1:10"
+	listValue := []string{"user1", "user2"}
+	listValueBytes, _ := json.Marshal(listValue)
+
+	t.Run("GetEntity", func(t *testing.T) {
+		mock.ExpectGet(entityKey).SetVal(string(valueBytes))
+		var result map[string]string
+		err := c.GetEntity(ctx, entityType, id, &result)
+		assert.NoError(t, err)
+		assert.Equal(t, value, result)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("SetEntity", func(t *testing.T) {
+		mock.ExpectSet(entityKey, valueBytes, time.Hour).SetVal("OK")
+		err := c.SetEntity(ctx, entityType, id, value, 0)
+		assert.NoError(t, err)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("DeleteEntity", func(t *testing.T) {
+		mock.ExpectDel(entityKey).SetVal(1)
+		err := c.DeleteEntity(ctx, entityType, id)
+		assert.NoError(t, err)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("GetList", func(t *testing.T) {
+		mock.ExpectGet(listKey).SetVal(string(listValueBytes))
+		var result []string
+		err := c.GetList(ctx, entityType, page, pageSize, &result)
+		assert.NoError(t, err)
+		assert.Equal(t, listValue, result)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("SetList", func(t *testing.T) {
+		mock.ExpectSet(listKey, listValueBytes, time.Hour).SetVal("OK")
+		err := c.SetList(ctx, entityType, page, pageSize, listValue, 0)
+		assert.NoError(t, err)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("DeleteList", func(t *testing.T) {
+		mock.ExpectDel(listKey).SetVal(1)
+		err := c.DeleteList(ctx, entityType, page, pageSize)
+		assert.NoError(t, err)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+}
+
+func TestRedisCache_Set(t *testing.T) {
+	client, mock := redismock.NewClientMock()
+	c := cache.NewRedisCache(client, nil, time.Hour)
+	ctx := context.Background()
+	key := "test-key"
+	value := map[string]string{"foo": "bar"}
+	expectedBytes, _ := json.Marshal(value)
+
+	t.Run("success with default expiration", func(t *testing.T) {
+		mock.ExpectSet(key, expectedBytes, time.Hour).SetVal("OK")
+
+		err := c.Set(ctx, key, value, 0)
+
+		assert.NoError(t, err)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("success with custom expiration", func(t *testing.T) {
+		expiration := 5 * time.Minute
+		mock.ExpectSet(key, expectedBytes, expiration).SetVal("OK")
+
+		err := c.Set(ctx, key, value, expiration)
+
+		assert.NoError(t, err)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("redis error", func(t *testing.T) {
+		mock.ExpectSet(key, expectedBytes, time.Hour).SetErr(errors.New("redis error"))
+
+		err := c.Set(ctx, key, value, 0)
+
+		assert.Error(t, err)
+		assert.Equal(t, "redis error", err.Error())
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+}
+
+func TestRedisCache_Delete(t *testing.T) {
+	client, mock := redismock.NewClientMock()
+	c := cache.NewRedisCache(client, nil, time.Hour)
+	ctx := context.Background()
+	key := "test-key"
+
+	t.Run("success", func(t *testing.T) {
+		mock.ExpectDel(key).SetVal(1)
+
+		err := c.Delete(ctx, key)
+
+		assert.NoError(t, err)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("redis error", func(t *testing.T) {
+		mock.ExpectDel(key).SetErr(errors.New("redis error"))
+
+		err := c.Delete(ctx, key)
+
+		assert.Error(t, err)
+		assert.Equal(t, "redis error", err.Error())
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+}
+
+func TestRedisCache_Clear(t *testing.T) {
+	client, mock := redismock.NewClientMock()
+	c := cache.NewRedisCache(client, nil, time.Hour)
+	ctx := context.Background()
+
+	t.Run("success", func(t *testing.T) {
+		mock.ExpectFlushAll().SetVal("OK")
+
+		err := c.Clear(ctx)
+
+		assert.NoError(t, err)
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+
+	t.Run("redis error", func(t *testing.T) {
+		mock.ExpectFlushAll().SetErr(errors.New("redis error"))
+
+		err := c.Clear(ctx)
+
+		assert.Error(t, err)
+		assert.Equal(t, "redis error", err.Error())
+		assert.NoError(t, mock.ExpectationsWereMet())
+	})
+}
\ No newline at end of file