diff --git a/backend/crates/postgres/Cargo.toml b/backend/crates/postgres/Cargo.toml
index b73ca89..de4abc8 100644
--- a/backend/crates/postgres/Cargo.toml
+++ b/backend/crates/postgres/Cargo.toml
@@ -12,3 +12,6 @@ sqlx = { workspace = true }
 tokio = { workspace = true }
 uuid = { workspace = true }
 chrono = { workspace = true }
+
+[dev-dependencies]
+futures = "0.3"
diff --git a/backend/crates/postgres/TEST_README.md b/backend/crates/postgres/TEST_README.md
new file mode 100644
index 0000000..a5cb155
--- /dev/null
+++ b/backend/crates/postgres/TEST_README.md
@@ -0,0 +1,206 @@
+# Postgres Crate Tests
+
+This document explains how to set up and run the unit tests for the postgres crate.
+
+## Prerequisites
+
+1. **PostgreSQL Database**: You need a PostgreSQL database running locally or remotely
+2. **Test Database**: Create a test database (e.g., `sharenet_test`)
+3. **Environment Variables**: Set up the `DATABASE_URL` environment variable
+
+## Setup
+
+### 1. Database Setup
+
+Create a test database:
+
+```sql
+CREATE DATABASE sharenet_test;
+```
+
+### 2. Environment Configuration
+
+Set the `DATABASE_URL` environment variable:
+
+```bash
+export DATABASE_URL="postgres://username:password@localhost:5432/sharenet_test"
+```
+
+Or create a `.env` file in the postgres crate directory:
+
+```env
+DATABASE_URL=postgres://username:password@localhost:5432/sharenet_test
+```
+
+### 3. SQLx Setup
+
+If you're using SQLx with offline mode, prepare the query cache:
+
+```bash
+cd backend/crates/postgres
+cargo sqlx prepare
+```
+
+## Migrations and Schema
+
+- The `users` table now enforces a unique constraint on the `username` field. This is implemented via a separate migration file:
+  - `20240101000001_add_username_unique_constraint.sql`
+- If you have already run previous migrations, make sure to apply the new migration:
+
+```bash
+cd backend/crates/postgres
+sqlx migrate run
+```
+
+## Running Tests
+
+### Run All Tests
+
+```bash
+cd backend/crates/postgres
+cargo test
+```
+
+### Run Specific Test Modules
+
+```bash
+# Run only user repository tests
+cargo test user_repository_tests
+
+# Run only product repository tests
+cargo test product_repository_tests
+
+# Run only service tests
+cargo test service_tests
+
+# Run only error handling tests
+cargo test error_handling_tests
+```
+
+### Run Tests with Output
+
+```bash
+cargo test -- --nocapture
+```
+
+## Test Isolation
+
+- The test setup function (`setup_test_db`) now always cleans up the database at the start of each test, ensuring a clean state for every test run.
+- For full isolation and to avoid concurrency issues, run tests with a single thread:
+
+```bash
+cargo test -- --test-threads=1
+```
+
+## Test Structure
+
+The tests are organized into the following modules:
+
+### 1. User Repository Tests (`user_repository_tests`)
+
+Tests for the `PostgresUserRepository` implementation:
+
+- **CRUD Operations**: Create, Read, Update, Delete users
+- **Error Handling**: Not found scenarios, duplicate constraints
+- **Edge Cases**: Empty results, partial updates
+
+### 2. Product Repository Tests (`product_repository_tests`)
+
+Tests for the `PostgresProductRepository` implementation:
+
+- **CRUD Operations**: Create, Read, Update, Delete products
+- **Error Handling**: Not found scenarios
+- **Edge Cases**: Empty results, partial updates
+
+### 3. Service Tests (`service_tests`)
+
+Tests for the service layer that wraps the repositories:
+
+- **Full Workflow**: Complete CRUD operations through services
+- **Integration**: Repository and service interaction
+
+### 4. Error Handling Tests (`error_handling_tests`)
+
+Tests for error scenarios:
+
+- **Database Connection**: Invalid connection strings
+- **Concurrent Access**: Multiple simultaneous operations
+
+## Test Database Management
+
+Each test automatically:
+
+1. **Sets up** a fresh database connection
+2. **Runs migrations** to ensure schema is up to date
+3. **Cleans up** test data after completion
+
+The test setup functions handle:
+- Database connection pooling
+- Migration execution
+- Data cleanup
+
+## Troubleshooting
+
+### Common Issues
+
+1. **Database Connection Failed**
+   - Verify PostgreSQL is running
+   - Check `DATABASE_URL` format
+   - Ensure database exists
+
+2. **Migration Errors**
+   - Ensure migrations are up to date
+   - Check database permissions
+
+3. **SQLx Compilation Errors**
+   - Run `cargo sqlx prepare` to update query cache
+   - Or set `DATABASE_URL` for online mode
+
+### Debug Mode
+
+To run tests with more verbose output:
+
+```bash
+RUST_LOG=debug cargo test -- --nocapture
+```
+
+## Test Data
+
+Tests use isolated data and clean up after themselves. Each test:
+
+- Creates its own test data
+- Verifies operations work correctly
+- Cleans up all created data
+
+This ensures tests are independent and don't interfere with each other.
+
+## Performance Considerations
+
+- Tests use a connection pool with max 5 connections
+- Each test runs in isolation
+- Database operations are async for better performance
+
+## Continuous Integration
+
+For CI/CD pipelines:
+
+1. Set up a PostgreSQL service container
+2. Configure `DATABASE_URL` environment variable
+3. Run `cargo test` in the postgres crate directory
+
+Example GitHub Actions setup:
+
+```yaml
+- name: Setup PostgreSQL
+  uses: Harmon758/postgresql-action@v1.0.0
+  with:
+    postgresql version: '15'
+    postgresql db: 'sharenet_test'
+
+- name: Run Postgres Tests
+  env:
+    DATABASE_URL: postgres://postgres:postgres@localhost:5432/sharenet_test
+  run: |
+    cd backend/crates/postgres
+    cargo test
+``` 
\ No newline at end of file
diff --git a/backend/crates/postgres/run_tests.sh b/backend/crates/postgres/run_tests.sh
new file mode 100644
index 0000000..4bc1917
--- /dev/null
+++ b/backend/crates/postgres/run_tests.sh
@@ -0,0 +1,123 @@
+#!/bin/bash
+
+# Postgres Crate Test Runner
+# This script helps set up and run the postgres crate tests
+
+set -e
+
+# Colors for output
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+YELLOW='\033[1;33m'
+NC='\033[0m' # No Color
+
+echo -e "${GREEN}Postgres Crate Test Runner${NC}"
+echo "================================"
+
+# Check if DATABASE_URL is set
+if [ -z "$DATABASE_URL" ]; then
+    echo -e "${YELLOW}DATABASE_URL not set, using default test database${NC}"
+    export DATABASE_URL="postgres://postgres:password@localhost:5432/sharenet_test"
+fi
+
+echo -e "${GREEN}Using database: $DATABASE_URL${NC}"
+
+# Check if we're in the right directory
+if [ ! -f "Cargo.toml" ] || [ ! -f "src/lib.rs" ]; then
+    echo -e "${RED}Error: Must run this script from the postgres crate directory${NC}"
+    echo "Current directory: $(pwd)"
+    echo "Expected files: Cargo.toml, src/lib.rs"
+    exit 1
+fi
+
+# Function to check if PostgreSQL is running
+check_postgres() {
+    echo -e "${YELLOW}Checking PostgreSQL connection...${NC}"
+    
+    # Try to connect to the database
+    if command -v psql &> /dev/null; then
+        if psql "$DATABASE_URL" -c "SELECT 1;" &> /dev/null; then
+            echo -e "${GREEN}PostgreSQL connection successful${NC}"
+            return 0
+        else
+            echo -e "${RED}PostgreSQL connection failed${NC}"
+            return 1
+        fi
+    else
+        echo -e "${YELLOW}psql not found, skipping connection check${NC}"
+        return 0
+    fi
+}
+
+# Function to run migrations
+run_migrations() {
+    echo -e "${YELLOW}Running database migrations...${NC}"
+    
+    if command -v sqlx &> /dev/null; then
+        sqlx migrate run --database-url "$DATABASE_URL" || {
+            echo -e "${RED}Migration failed${NC}"
+            return 1
+        }
+        echo -e "${GREEN}Migrations completed successfully${NC}"
+    else
+        echo -e "${YELLOW}sqlx CLI not found, migrations will be run by tests${NC}"
+    fi
+}
+
+# Function to run tests
+run_tests() {
+    echo -e "${GREEN}Running tests...${NC}"
+    
+    # Check if specific test pattern was provided
+    if [ $# -eq 0 ]; then
+        echo "Running all tests..."
+        cargo test
+    else
+        echo "Running tests matching: $1"
+        cargo test "$1"
+    fi
+}
+
+# Main execution
+main() {
+    # Check PostgreSQL connection
+    if ! check_postgres; then
+        echo -e "${RED}Please ensure PostgreSQL is running and accessible${NC}"
+        echo "You can start PostgreSQL with:"
+        echo "  sudo systemctl start postgresql"
+        echo "  or"
+        echo "  docker run --name postgres-test -e POSTGRES_PASSWORD=password -e POSTGRES_DB=sharenet_test -p 5432:5432 -d postgres:15"
+        exit 1
+    fi
+    
+    # Run migrations
+    run_migrations
+    
+    # Run tests
+    run_tests "$@"
+    
+    echo -e "${GREEN}Tests completed!${NC}"
+}
+
+# Handle command line arguments
+case "${1:-}" in
+    --help|-h)
+        echo "Usage: $0 [test_pattern]"
+        echo ""
+        echo "Options:"
+        echo "  test_pattern    Run only tests matching this pattern"
+        echo "  --help, -h      Show this help message"
+        echo ""
+        echo "Examples:"
+        echo "  $0                    # Run all tests"
+        echo "  $0 user_repository    # Run user repository tests"
+        echo "  $0 create             # Run tests with 'create' in the name"
+        echo ""
+        echo "Environment:"
+        echo "  DATABASE_URL          Database connection string (optional)"
+        exit 0
+        ;;
+    *)
+        main "$@"
+        ;;
+esac 
\ No newline at end of file
diff --git a/backend/crates/postgres/src/lib.rs b/backend/crates/postgres/src/lib.rs
index 278dee2..4e33475 100644
--- a/backend/crates/postgres/src/lib.rs
+++ b/backend/crates/postgres/src/lib.rs
@@ -233,3 +233,694 @@ impl Repository<Product> for PostgresProductRepository {
 
 pub type PostgresUserService = Service<User, PostgresUserRepository>;
 pub type PostgresProductService = Service<Product, PostgresProductRepository>;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use sqlx::PgPool;
+    use sqlx::postgres::PgPoolOptions;
+    use std::env;
+    use chrono::Utc;
+
+    // Test database setup
+    async fn setup_test_db() -> PgPool {
+        let database_url = env::var("DATABASE_URL")
+            .unwrap_or_else(|_| "postgres://postgres:password@localhost:5432/sharenet_test".to_string());
+        
+        let pool = PgPoolOptions::new()
+            .max_connections(5)
+            .connect(&database_url)
+            .await
+            .expect("Failed to connect to test database");
+
+        // Run migrations
+        sqlx::migrate!("../../migrations")
+            .run(&pool)
+            .await
+            .expect("Failed to run migrations");
+
+        // Clean up any existing test data
+        cleanup_test_data(&pool).await;
+
+        pool
+    }
+
+    // Clean up test data
+    async fn cleanup_test_data(pool: &PgPool) {
+        sqlx::query("DELETE FROM products").execute(pool).await.ok();
+        sqlx::query("DELETE FROM users").execute(pool).await.ok();
+    }
+
+    mod user_repository_tests {
+        use super::*;
+
+        #[tokio::test]
+        async fn test_create_user() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            
+            let create_data = CreateUser {
+                username: "testuser".to_string(),
+                email: "test@example.com".to_string(),
+            };
+
+            let result = repo.create(create_data).await;
+            assert!(result.is_ok());
+
+            let user = result.unwrap();
+            assert_eq!(user.username, "testuser");
+            assert_eq!(user.email, "test@example.com");
+            assert!(user.id != Uuid::nil());
+            assert!(user.created_at <= Utc::now());
+            assert!(user.updated_at <= Utc::now());
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_create_user_with_duplicate_username() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            
+            let create_data = CreateUser {
+                username: "duplicate_user".to_string(),
+                email: "test1@example.com".to_string(),
+            };
+
+            // Create first user
+            let result1 = repo.create(create_data.clone()).await;
+            assert!(result1.is_ok());
+
+            // Try to create second user with same username
+            let create_data2 = CreateUser {
+                username: "duplicate_user".to_string(),
+                email: "test2@example.com".to_string(),
+            };
+            let result2 = repo.create(create_data2).await;
+            assert!(result2.is_err());
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_find_user_by_id() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            
+            let create_data = CreateUser {
+                username: "finduser".to_string(),
+                email: "find@example.com".to_string(),
+            };
+
+            let created_user = repo.create(create_data).await.unwrap();
+            let found_user = repo.find_by_id(created_user.id).await;
+            
+            assert!(found_user.is_ok());
+            let user = found_user.unwrap();
+            assert_eq!(user.id, created_user.id);
+            assert_eq!(user.username, "finduser");
+            assert_eq!(user.email, "find@example.com");
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_find_user_by_nonexistent_id() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            
+            let nonexistent_id = Uuid::new_v4();
+            let result = repo.find_by_id(nonexistent_id).await;
+            
+            assert!(result.is_err());
+            match result.unwrap_err() {
+                domain::DomainError::NotFound(msg) => {
+                    assert!(msg.contains("User not found"));
+                }
+                _ => panic!("Expected NotFound error"),
+            }
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_find_all_users() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            
+            // Create multiple users
+            let _user1 = repo.create(CreateUser {
+                username: "user1".to_string(),
+                email: "user1@example.com".to_string(),
+            }).await.unwrap();
+
+            let _user2 = repo.create(CreateUser {
+                username: "user2".to_string(),
+                email: "user2@example.com".to_string(),
+            }).await.unwrap();
+
+            let users = repo.find_all().await.unwrap();
+            assert_eq!(users.len(), 2);
+            
+            let usernames: Vec<String> = users.iter().map(|u| u.username.clone()).collect();
+            assert!(usernames.contains(&"user1".to_string()));
+            assert!(usernames.contains(&"user2".to_string()));
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_find_all_users_empty() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            
+            let users = repo.find_all().await.unwrap();
+            assert_eq!(users.len(), 0);
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_update_user() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            
+            let create_data = CreateUser {
+                username: "updateuser".to_string(),
+                email: "update@example.com".to_string(),
+            };
+
+            let user = repo.create(create_data).await.unwrap();
+            let original_updated_at = user.updated_at;
+
+            // Update username only
+            let update_data = UpdateUser {
+                username: Some("updateduser".to_string()),
+                email: None,
+            };
+
+            let updated_user = repo.update(user.id, update_data).await.unwrap();
+            assert_eq!(updated_user.username, "updateduser");
+            assert_eq!(updated_user.email, "update@example.com"); // Should remain unchanged
+            assert!(updated_user.updated_at > original_updated_at);
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_update_user_email_only() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            
+            let create_data = CreateUser {
+                username: "emailuser".to_string(),
+                email: "old@example.com".to_string(),
+            };
+
+            let user = repo.create(create_data).await.unwrap();
+
+            let update_data = UpdateUser {
+                username: None,
+                email: Some("new@example.com".to_string()),
+            };
+
+            let updated_user = repo.update(user.id, update_data).await.unwrap();
+            assert_eq!(updated_user.username, "emailuser"); // Should remain unchanged
+            assert_eq!(updated_user.email, "new@example.com");
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_update_user_both_fields() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            
+            let create_data = CreateUser {
+                username: "bothuser".to_string(),
+                email: "both@example.com".to_string(),
+            };
+
+            let user = repo.create(create_data).await.unwrap();
+
+            let update_data = UpdateUser {
+                username: Some("newbothuser".to_string()),
+                email: Some("newboth@example.com".to_string()),
+            };
+
+            let updated_user = repo.update(user.id, update_data).await.unwrap();
+            assert_eq!(updated_user.username, "newbothuser");
+            assert_eq!(updated_user.email, "newboth@example.com");
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_update_nonexistent_user() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            
+            let nonexistent_id = Uuid::new_v4();
+            let update_data = UpdateUser {
+                username: Some("nonexistent".to_string()),
+                email: None,
+            };
+
+            let result = repo.update(nonexistent_id, update_data).await;
+            assert!(result.is_err());
+            match result.unwrap_err() {
+                domain::DomainError::NotFound(msg) => {
+                    assert!(msg.contains("User not found"));
+                }
+                _ => panic!("Expected NotFound error"),
+            }
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_delete_user() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            
+            let create_data = CreateUser {
+                username: "deleteuser".to_string(),
+                email: "delete@example.com".to_string(),
+            };
+
+            let user = repo.create(create_data).await.unwrap();
+            let user_id = user.id;
+
+            // Verify user exists
+            let found_user = repo.find_by_id(user_id).await;
+            assert!(found_user.is_ok());
+
+            // Delete user
+            let delete_result = repo.delete(user_id).await;
+            assert!(delete_result.is_ok());
+
+            // Verify user no longer exists
+            let found_user_after_delete = repo.find_by_id(user_id).await;
+            assert!(found_user_after_delete.is_err());
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_delete_nonexistent_user() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            
+            let nonexistent_id = Uuid::new_v4();
+            let result = repo.delete(nonexistent_id).await;
+            
+            assert!(result.is_err());
+            match result.unwrap_err() {
+                domain::DomainError::NotFound(msg) => {
+                    assert!(msg.contains("User not found"));
+                }
+                _ => panic!("Expected NotFound error"),
+            }
+
+            cleanup_test_data(&pool).await;
+        }
+    }
+
+    mod product_repository_tests {
+        use super::*;
+
+        #[tokio::test]
+        async fn test_create_product() {
+            let pool = setup_test_db().await;
+            let repo = PostgresProductRepository::new(pool.clone());
+            
+            let create_data = CreateProduct {
+                name: "Test Product".to_string(),
+                description: "Test Description".to_string(),
+            };
+
+            let result = repo.create(create_data).await;
+            assert!(result.is_ok());
+
+            let product = result.unwrap();
+            assert_eq!(product.name, "Test Product");
+            assert_eq!(product.description, "Test Description");
+            assert!(product.id != Uuid::nil());
+            assert!(product.created_at <= Utc::now());
+            assert!(product.updated_at <= Utc::now());
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_find_product_by_id() {
+            let pool = setup_test_db().await;
+            let repo = PostgresProductRepository::new(pool.clone());
+            
+            let create_data = CreateProduct {
+                name: "Find Product".to_string(),
+                description: "Find Description".to_string(),
+            };
+
+            let created_product = repo.create(create_data).await.unwrap();
+            let found_product = repo.find_by_id(created_product.id).await;
+            
+            assert!(found_product.is_ok());
+            let product = found_product.unwrap();
+            assert_eq!(product.id, created_product.id);
+            assert_eq!(product.name, "Find Product");
+            assert_eq!(product.description, "Find Description");
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_find_product_by_nonexistent_id() {
+            let pool = setup_test_db().await;
+            let repo = PostgresProductRepository::new(pool.clone());
+            
+            let nonexistent_id = Uuid::new_v4();
+            let result = repo.find_by_id(nonexistent_id).await;
+            
+            assert!(result.is_err());
+            match result.unwrap_err() {
+                domain::DomainError::NotFound(msg) => {
+                    assert!(msg.contains("Product not found"));
+                }
+                _ => panic!("Expected NotFound error"),
+            }
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_find_all_products() {
+            let pool = setup_test_db().await;
+            let repo = PostgresProductRepository::new(pool.clone());
+            
+            // Create multiple products
+            let _product1 = repo.create(CreateProduct {
+                name: "Product 1".to_string(),
+                description: "Description 1".to_string(),
+            }).await.unwrap();
+
+            let _product2 = repo.create(CreateProduct {
+                name: "Product 2".to_string(),
+                description: "Description 2".to_string(),
+            }).await.unwrap();
+
+            let products = repo.find_all().await.unwrap();
+            assert_eq!(products.len(), 2);
+            
+            let names: Vec<String> = products.iter().map(|p| p.name.clone()).collect();
+            assert!(names.contains(&"Product 1".to_string()));
+            assert!(names.contains(&"Product 2".to_string()));
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_find_all_products_empty() {
+            let pool = setup_test_db().await;
+            let repo = PostgresProductRepository::new(pool.clone());
+            
+            let products = repo.find_all().await.unwrap();
+            assert_eq!(products.len(), 0);
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_update_product() {
+            let pool = setup_test_db().await;
+            let repo = PostgresProductRepository::new(pool.clone());
+            
+            let create_data = CreateProduct {
+                name: "Update Product".to_string(),
+                description: "Update Description".to_string(),
+            };
+
+            let product = repo.create(create_data).await.unwrap();
+            let original_updated_at = product.updated_at;
+
+            // Update name only
+            let update_data = UpdateProduct {
+                name: Some("Updated Product".to_string()),
+                description: None,
+            };
+
+            let updated_product = repo.update(product.id, update_data).await.unwrap();
+            assert_eq!(updated_product.name, "Updated Product");
+            assert_eq!(updated_product.description, "Update Description"); // Should remain unchanged
+            assert!(updated_product.updated_at > original_updated_at);
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_update_product_description_only() {
+            let pool = setup_test_db().await;
+            let repo = PostgresProductRepository::new(pool.clone());
+            
+            let create_data = CreateProduct {
+                name: "Desc Product".to_string(),
+                description: "Old Description".to_string(),
+            };
+
+            let product = repo.create(create_data).await.unwrap();
+
+            let update_data = UpdateProduct {
+                name: None,
+                description: Some("New Description".to_string()),
+            };
+
+            let updated_product = repo.update(product.id, update_data).await.unwrap();
+            assert_eq!(updated_product.name, "Desc Product"); // Should remain unchanged
+            assert_eq!(updated_product.description, "New Description");
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_update_product_both_fields() {
+            let pool = setup_test_db().await;
+            let repo = PostgresProductRepository::new(pool.clone());
+            
+            let create_data = CreateProduct {
+                name: "Both Product".to_string(),
+                description: "Both Description".to_string(),
+            };
+
+            let product = repo.create(create_data).await.unwrap();
+
+            let update_data = UpdateProduct {
+                name: Some("New Both Product".to_string()),
+                description: Some("New Both Description".to_string()),
+            };
+
+            let updated_product = repo.update(product.id, update_data).await.unwrap();
+            assert_eq!(updated_product.name, "New Both Product");
+            assert_eq!(updated_product.description, "New Both Description");
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_update_nonexistent_product() {
+            let pool = setup_test_db().await;
+            let repo = PostgresProductRepository::new(pool.clone());
+            
+            let nonexistent_id = Uuid::new_v4();
+            let update_data = UpdateProduct {
+                name: Some("Nonexistent Product".to_string()),
+                description: None,
+            };
+
+            let result = repo.update(nonexistent_id, update_data).await;
+            assert!(result.is_err());
+            match result.unwrap_err() {
+                domain::DomainError::NotFound(msg) => {
+                    assert!(msg.contains("Product not found"));
+                }
+                _ => panic!("Expected NotFound error"),
+            }
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_delete_product() {
+            let pool = setup_test_db().await;
+            let repo = PostgresProductRepository::new(pool.clone());
+            
+            let create_data = CreateProduct {
+                name: "Delete Product".to_string(),
+                description: "Delete Description".to_string(),
+            };
+
+            let product = repo.create(create_data).await.unwrap();
+            let product_id = product.id;
+
+            // Verify product exists
+            let found_product = repo.find_by_id(product_id).await;
+            assert!(found_product.is_ok());
+
+            // Delete product
+            let delete_result = repo.delete(product_id).await;
+            assert!(delete_result.is_ok());
+
+            // Verify product no longer exists
+            let found_product_after_delete = repo.find_by_id(product_id).await;
+            assert!(found_product_after_delete.is_err());
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_delete_nonexistent_product() {
+            let pool = setup_test_db().await;
+            let repo = PostgresProductRepository::new(pool.clone());
+            
+            let nonexistent_id = Uuid::new_v4();
+            let result = repo.delete(nonexistent_id).await;
+            
+            assert!(result.is_err());
+            match result.unwrap_err() {
+                domain::DomainError::NotFound(msg) => {
+                    assert!(msg.contains("Product not found"));
+                }
+                _ => panic!("Expected NotFound error"),
+            }
+
+            cleanup_test_data(&pool).await;
+        }
+    }
+
+    mod service_tests {
+        use super::*;
+        use application::UseCase;
+
+        #[tokio::test]
+        async fn test_postgres_user_service() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            let service = PostgresUserService::new(repo);
+            
+            let create_data = CreateUser {
+                username: "serviceuser".to_string(),
+                email: "service@example.com".to_string(),
+            };
+
+            // Test create
+            let user = service.create(create_data).await.unwrap();
+            assert_eq!(user.username, "serviceuser");
+
+            // Test get
+            let found_user = service.get(user.id).await.unwrap();
+            assert_eq!(found_user.id, user.id);
+
+            // Test list
+            let users = service.list().await.unwrap();
+            assert_eq!(users.len(), 1);
+
+            // Test update
+            let update_data = UpdateUser {
+                username: Some("updatedserviceuser".to_string()),
+                email: None,
+            };
+            let updated_user = service.update(user.id, update_data).await.unwrap();
+            assert_eq!(updated_user.username, "updatedserviceuser");
+
+            // Test delete
+            let delete_result = service.delete(user.id).await;
+            assert!(delete_result.is_ok());
+
+            cleanup_test_data(&pool).await;
+        }
+
+        #[tokio::test]
+        async fn test_postgres_product_service() {
+            let pool = setup_test_db().await;
+            let repo = PostgresProductRepository::new(pool.clone());
+            let service = PostgresProductService::new(repo);
+            
+            let create_data = CreateProduct {
+                name: "Service Product".to_string(),
+                description: "Service Description".to_string(),
+            };
+
+            // Test create
+            let product = service.create(create_data).await.unwrap();
+            assert_eq!(product.name, "Service Product");
+
+            // Test get
+            let found_product = service.get(product.id).await.unwrap();
+            assert_eq!(found_product.id, product.id);
+
+            // Test list
+            let products = service.list().await.unwrap();
+            assert_eq!(products.len(), 1);
+
+            // Test update
+            let update_data = UpdateProduct {
+                name: Some("Updated Service Product".to_string()),
+                description: None,
+            };
+            let updated_product = service.update(product.id, update_data).await.unwrap();
+            assert_eq!(updated_product.name, "Updated Service Product");
+
+            // Test delete
+            let delete_result = service.delete(product.id).await;
+            assert!(delete_result.is_ok());
+
+            cleanup_test_data(&pool).await;
+        }
+    }
+
+    mod error_handling_tests {
+        use super::*;
+
+        #[tokio::test]
+        async fn test_database_connection_error() {
+            // Test with invalid database URL
+            let invalid_pool = PgPoolOptions::new()
+                .max_connections(1)
+                .connect("postgres://invalid:invalid@localhost:5432/nonexistent")
+                .await;
+
+            assert!(invalid_pool.is_err());
+        }
+
+        #[tokio::test]
+        async fn test_concurrent_access() {
+            let pool = setup_test_db().await;
+            let repo = PostgresUserRepository::new(pool.clone());
+            
+            let create_data = CreateUser {
+                username: "concurrentuser".to_string(),
+                email: "concurrent@example.com".to_string(),
+            };
+
+            // Create a user
+            let user = repo.create(create_data).await.unwrap();
+
+            // Simulate concurrent reads
+            let handles: Vec<_> = (0..10)
+                .map(|_| {
+                    let repo_clone = repo.clone();
+                    let user_id = user.id;
+                    tokio::spawn(async move {
+                        repo_clone.find_by_id(user_id).await
+                    })
+                })
+                .collect();
+
+            let results = futures::future::join_all(handles).await;
+            for result in results {
+                assert!(result.unwrap().is_ok());
+            }
+
+            cleanup_test_data(&pool).await;
+        }
+    }
+}
diff --git a/backend/crates/postgres/tests/integration_test_setup.rs b/backend/crates/postgres/tests/integration_test_setup.rs
new file mode 100644
index 0000000..a5285e8
--- /dev/null
+++ b/backend/crates/postgres/tests/integration_test_setup.rs
@@ -0,0 +1,43 @@
+/*
+ * This file is part of Sharenet.
+ * 
+ * Sharenet is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
+ * 
+ * You may obtain a copy of the license at:
+ * https://creativecommons.org/licenses/by-nc-sa/4.0/
+ * 
+ * Copyright (c) 2024 Continuist <continuist02@gmail.com>
+ */
+
+use sqlx::PgPool;
+use sqlx::postgres::PgPoolOptions;
+use std::env;
+
+pub async fn setup_test_database() -> PgPool {
+    let database_url = env::var("DATABASE_URL")
+        .unwrap_or_else(|_| "postgres://postgres:postgres@localhost:5432/sharenet_test".to_string());
+    
+    let pool = PgPoolOptions::new()
+        .max_connections(5)
+        .connect(&database_url)
+        .await
+        .expect("Failed to connect to test database");
+
+    // Run migrations
+    sqlx::migrate!("../../migrations")
+        .run(&pool)
+        .await
+        .expect("Failed to run migrations");
+
+    pool
+}
+
+pub async fn cleanup_test_data(pool: &PgPool) {
+    sqlx::query("DELETE FROM products").execute(pool).await.ok();
+    sqlx::query("DELETE FROM users").execute(pool).await.ok();
+}
+
+pub fn get_test_database_url() -> String {
+    env::var("DATABASE_URL")
+        .unwrap_or_else(|_| "postgres://postgres:postgres@localhost:5432/sharenet_test".to_string())
+} 
\ No newline at end of file
diff --git a/backend/migrations/20240101000001_add_username_unique_constraint.sql b/backend/migrations/20240101000001_add_username_unique_constraint.sql
new file mode 100644
index 0000000..3b13558
--- /dev/null
+++ b/backend/migrations/20240101000001_add_username_unique_constraint.sql
@@ -0,0 +1,2 @@
+-- Add unique constraint to username field
+ALTER TABLE users ADD CONSTRAINT users_username_unique UNIQUE (username); 
\ No newline at end of file