diff --git a/backend/crates/cli/Cargo.toml b/backend/crates/cli/Cargo.toml
index bc2ccc4..54521ae 100644
--- a/backend/crates/cli/Cargo.toml
+++ b/backend/crates/cli/Cargo.toml
@@ -14,6 +14,7 @@ tokio = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
 uuid = { workspace = true }
-ratatui = { workspace = true }
 crossterm = { workspace = true }
 textwrap = "0.16"
+chrono = { workspace = true }
+thiserror = { workspace = true }
diff --git a/backend/crates/cli/src/lib.rs b/backend/crates/cli/src/lib.rs
index cea65cc..a42d6e8 100644
--- a/backend/crates/cli/src/lib.rs
+++ b/backend/crates/cli/src/lib.rs
@@ -174,3 +174,967 @@ impl Cli {
         Ok(())
     }
 }
+
+#[cfg(test)]
+mod tests {
+    //! # CLI Tests
+    //!
+    //! This module contains comprehensive unit tests for the CLI application.
+    //! Tests cover command parsing, execution, and error handling scenarios.
+    //!
+    //! ## Test Structure
+    //! - `command_parsing` - Tests for CLI argument parsing
+    //! - `user_commands` - Tests for user management commands
+    //! - `product_commands` - Tests for product management commands
+    //! - `integration_tests` - End-to-end command execution tests
+    //! - `error_handling` - Tests for error scenarios
+    //!
+    //! ## Testing Approach
+    //! - Uses mock services implementing the `UseCase` trait
+    //! - Tests verify command parsing and execution
+    //! - Captures stdout to verify output messages
+    //! - Tests error handling and edge cases
+
+    use super::*;
+    use application::{UseCase, ApplicationError};
+    use domain::{DomainError, User, Product, CreateUser, UpdateUser, CreateProduct, UpdateProduct};
+    use std::sync::Arc;
+    use tokio::sync::RwLock;
+    use std::collections::HashMap;
+    use chrono::Utc;
+
+    /// Mock user service for testing.
+    ///
+    /// Implements the `UseCase<User>` trait using an in-memory HashMap
+    /// for storing test data. Provides thread-safe access via `RwLock`.
+    #[derive(Clone)]
+    struct MockUserService {
+        users: Arc<RwLock<HashMap<Uuid, User>>>,
+    }
+
+    impl MockUserService {
+        fn new() -> Self {
+            Self {
+                users: Arc::new(RwLock::new(HashMap::new())),
+            }
+        }
+    }
+
+    impl UseCase<User> for MockUserService {
+        fn create(&self, data: CreateUser) -> impl std::future::Future<Output = Result<User, ApplicationError>> + Send {
+            let users = self.users.clone();
+            async move {
+                let mut guard = users.write().await;
+                let id = Uuid::new_v4();
+                let user = User {
+                    id,
+                    username: data.username,
+                    email: data.email,
+                    created_at: Utc::now(),
+                    updated_at: Utc::now(),
+                };
+                guard.insert(id, user.clone());
+                Ok(user)
+            }
+        }
+
+        fn get(&self, id: Uuid) -> impl std::future::Future<Output = Result<User, ApplicationError>> + Send {
+            let users = self.users.clone();
+            async move {
+                let guard = users.read().await;
+                guard.get(&id)
+                    .cloned()
+                    .ok_or_else(|| ApplicationError::Domain(DomainError::NotFound(format!("User not found: {}", id))))
+            }
+        }
+
+        fn list(&self) -> impl std::future::Future<Output = Result<Vec<User>, ApplicationError>> + Send {
+            let users = self.users.clone();
+            async move {
+                let guard = users.read().await;
+                Ok(guard.values().cloned().collect())
+            }
+        }
+
+        fn update(&self, id: Uuid, data: UpdateUser) -> impl std::future::Future<Output = Result<User, ApplicationError>> + Send {
+            let users = self.users.clone();
+            async move {
+                let mut guard = users.write().await;
+                let user = guard.get_mut(&id)
+                    .ok_or_else(|| ApplicationError::Domain(DomainError::NotFound(format!("User not found: {}", id))))?;
+                
+                if let Some(username) = data.username {
+                    user.username = username;
+                }
+                if let Some(email) = data.email {
+                    user.email = email;
+                }
+                user.updated_at = Utc::now();
+                Ok(user.clone())
+            }
+        }
+
+        fn delete(&self, id: Uuid) -> impl std::future::Future<Output = Result<(), ApplicationError>> + Send {
+            let users = self.users.clone();
+            async move {
+                let mut guard = users.write().await;
+                guard.remove(&id)
+                    .ok_or_else(|| ApplicationError::Domain(DomainError::NotFound(format!("User not found: {}", id))))?;
+                Ok(())
+            }
+        }
+    }
+
+    /// Mock product service for testing.
+    ///
+    /// Implements the `UseCase<Product>` trait using an in-memory HashMap
+    /// for storing test data. Provides thread-safe access via `RwLock`.
+    #[derive(Clone)]
+    struct MockProductService {
+        products: Arc<RwLock<HashMap<Uuid, Product>>>,
+    }
+
+    impl MockProductService {
+        fn new() -> Self {
+            Self {
+                products: Arc::new(RwLock::new(HashMap::new())),
+            }
+        }
+    }
+
+    impl UseCase<Product> for MockProductService {
+        fn create(&self, data: CreateProduct) -> impl std::future::Future<Output = Result<Product, ApplicationError>> + Send {
+            let products = self.products.clone();
+            async move {
+                let mut guard = products.write().await;
+                let id = Uuid::new_v4();
+                let product = Product {
+                    id,
+                    name: data.name,
+                    description: data.description,
+                    created_at: Utc::now(),
+                    updated_at: Utc::now(),
+                };
+                guard.insert(id, product.clone());
+                Ok(product)
+            }
+        }
+
+        fn get(&self, id: Uuid) -> impl std::future::Future<Output = Result<Product, ApplicationError>> + Send {
+            let products = self.products.clone();
+            async move {
+                let guard = products.read().await;
+                guard.get(&id)
+                    .cloned()
+                    .ok_or_else(|| ApplicationError::Domain(DomainError::NotFound(format!("Product not found: {}", id))))
+            }
+        }
+
+        fn list(&self) -> impl std::future::Future<Output = Result<Vec<Product>, ApplicationError>> + Send {
+            let products = self.products.clone();
+            async move {
+                let guard = products.read().await;
+                Ok(guard.values().cloned().collect())
+            }
+        }
+
+        fn update(&self, id: Uuid, data: UpdateProduct) -> impl std::future::Future<Output = Result<Product, ApplicationError>> + Send {
+            let products = self.products.clone();
+            async move {
+                let mut guard = products.write().await;
+                let product = guard.get_mut(&id)
+                    .ok_or_else(|| ApplicationError::Domain(DomainError::NotFound(format!("Product not found: {}", id))))?;
+                
+                if let Some(name) = data.name {
+                    product.name = name;
+                }
+                if let Some(description) = data.description {
+                    product.description = description;
+                }
+                product.updated_at = Utc::now();
+                Ok(product.clone())
+            }
+        }
+
+        fn delete(&self, id: Uuid) -> impl std::future::Future<Output = Result<(), ApplicationError>> + Send {
+            let products = self.products.clone();
+            async move {
+                let mut guard = products.write().await;
+                guard.remove(&id)
+                    .ok_or_else(|| ApplicationError::Domain(DomainError::NotFound(format!("Product not found: {}", id))))?;
+                Ok(())
+            }
+        }
+    }
+
+    mod command_parsing {
+        use super::*;
+
+        /// Tests that the CLI can parse user create command with all arguments.
+        #[test]
+        fn test_parse_user_create() {
+            let args = vec![
+                "cli",
+                "user",
+                "create",
+                "--username", "testuser",
+                "--email", "test@example.com"
+            ];
+
+            let cli = Cli::try_parse_from(args).unwrap();
+            
+            if let Some(Commands::User { command: UserCommands::Create { username, email } }) = cli.command {
+                assert_eq!(username, "testuser");
+                assert_eq!(email, "test@example.com");
+            } else {
+                panic!("Expected user create command");
+            }
+        }
+
+        /// Tests that the CLI can parse user create command with short arguments.
+        #[test]
+        fn test_parse_user_create_short_args() {
+            let args = vec![
+                "cli",
+                "user",
+                "create",
+                "-u", "testuser",
+                "-e", "test@example.com"
+            ];
+
+            let cli = Cli::try_parse_from(args).unwrap();
+            
+            if let Some(Commands::User { command: UserCommands::Create { username, email } }) = cli.command {
+                assert_eq!(username, "testuser");
+                assert_eq!(email, "test@example.com");
+            } else {
+                panic!("Expected user create command");
+            }
+        }
+
+        /// Tests that the CLI can parse user list command.
+        #[test]
+        fn test_parse_user_list() {
+            let args = vec!["cli", "user", "list"];
+
+            let cli = Cli::try_parse_from(args).unwrap();
+            
+            if let Some(Commands::User { command: UserCommands::List }) = cli.command {
+                // Command parsed successfully
+            } else {
+                panic!("Expected user list command");
+            }
+        }
+
+        /// Tests that the CLI can parse user get command.
+        #[test]
+        fn test_parse_user_get() {
+            let user_id = Uuid::new_v4();
+            let user_id_str = user_id.to_string();
+            let args = vec![
+                "cli",
+                "user",
+                "get",
+                "--id", &user_id_str
+            ];
+
+            let cli = Cli::try_parse_from(args).unwrap();
+            
+            if let Some(Commands::User { command: UserCommands::Get { id } }) = cli.command {
+                assert_eq!(id, user_id);
+            } else {
+                panic!("Expected user get command");
+            }
+        }
+
+        /// Tests that the CLI can parse user update command with all fields.
+        #[test]
+        fn test_parse_user_update() {
+            let user_id = Uuid::new_v4();
+            let user_id_str = user_id.to_string();
+            let args = vec![
+                "cli",
+                "user",
+                "update",
+                "--id", &user_id_str,
+                "--username", "newuser",
+                "--email", "new@example.com"
+            ];
+
+            let cli = Cli::try_parse_from(args).unwrap();
+            
+            if let Some(Commands::User { command: UserCommands::Update { id, username, email } }) = cli.command {
+                assert_eq!(id, user_id);
+                assert_eq!(username, Some("newuser".to_string()));
+                assert_eq!(email, Some("new@example.com".to_string()));
+            } else {
+                panic!("Expected user update command");
+            }
+        }
+
+        /// Tests that the CLI can parse user update command with partial fields.
+        #[test]
+        fn test_parse_user_update_partial() {
+            let user_id = Uuid::new_v4();
+            let user_id_str = user_id.to_string();
+            let args = vec![
+                "cli",
+                "user",
+                "update",
+                "--id", &user_id_str,
+                "--username", "newuser"
+            ];
+
+            let cli = Cli::try_parse_from(args).unwrap();
+            
+            if let Some(Commands::User { command: UserCommands::Update { id, username, email } }) = cli.command {
+                assert_eq!(id, user_id);
+                assert_eq!(username, Some("newuser".to_string()));
+                assert_eq!(email, None);
+            } else {
+                panic!("Expected user update command");
+            }
+        }
+
+        /// Tests that the CLI can parse user delete command.
+        #[test]
+        fn test_parse_user_delete() {
+            let user_id = Uuid::new_v4();
+            let user_id_str = user_id.to_string();
+            let args = vec![
+                "cli",
+                "user",
+                "delete",
+                "--id", &user_id_str
+            ];
+
+            let cli = Cli::try_parse_from(args).unwrap();
+            
+            if let Some(Commands::User { command: UserCommands::Delete { id } }) = cli.command {
+                assert_eq!(id, user_id);
+            } else {
+                panic!("Expected user delete command");
+            }
+        }
+
+        /// Tests that the CLI can parse product create command.
+        #[test]
+        fn test_parse_product_create() {
+            let args = vec![
+                "cli",
+                "product",
+                "create",
+                "--name", "Test Product",
+                "--description", "Test Description"
+            ];
+
+            let cli = Cli::try_parse_from(args).unwrap();
+            
+            if let Some(Commands::Product { command: ProductCommands::Create { name, description } }) = cli.command {
+                assert_eq!(name, "Test Product");
+                assert_eq!(description, "Test Description");
+            } else {
+                panic!("Expected product create command");
+            }
+        }
+
+        /// Tests that the CLI can parse product list command.
+        #[test]
+        fn test_parse_product_list() {
+            let args = vec!["cli", "product", "list"];
+
+            let cli = Cli::try_parse_from(args).unwrap();
+            
+            if let Some(Commands::Product { command: ProductCommands::List }) = cli.command {
+                // Command parsed successfully
+            } else {
+                panic!("Expected product list command");
+            }
+        }
+
+        /// Tests that the CLI can parse product get command.
+        #[test]
+        fn test_parse_product_get() {
+            let product_id = Uuid::new_v4();
+            let product_id_str = product_id.to_string();
+            let args = vec![
+                "cli",
+                "product",
+                "get",
+                "--id", &product_id_str
+            ];
+
+            let cli = Cli::try_parse_from(args).unwrap();
+            
+            if let Some(Commands::Product { command: ProductCommands::Get { id } }) = cli.command {
+                assert_eq!(id, product_id);
+            } else {
+                panic!("Expected product get command");
+            }
+        }
+
+        /// Tests that the CLI can parse product update command.
+        #[test]
+        fn test_parse_product_update() {
+            let product_id = Uuid::new_v4();
+            let product_id_str = product_id.to_string();
+            let args = vec![
+                "cli",
+                "product",
+                "update",
+                "--id", &product_id_str,
+                "--name", "New Product",
+                "--description", "New Description"
+            ];
+
+            let cli = Cli::try_parse_from(args).unwrap();
+            
+            if let Some(Commands::Product { command: ProductCommands::Update { id, name, description } }) = cli.command {
+                assert_eq!(id, product_id);
+                assert_eq!(name, Some("New Product".to_string()));
+                assert_eq!(description, Some("New Description".to_string()));
+            } else {
+                panic!("Expected product update command");
+            }
+        }
+
+        /// Tests that the CLI can parse product delete command.
+        #[test]
+        fn test_parse_product_delete() {
+            let product_id = Uuid::new_v4();
+            let product_id_str = product_id.to_string();
+            let args = vec![
+                "cli",
+                "product",
+                "delete",
+                "--id", &product_id_str
+            ];
+
+            let cli = Cli::try_parse_from(args).unwrap();
+            
+            if let Some(Commands::Product { command: ProductCommands::Delete { id } }) = cli.command {
+                assert_eq!(id, product_id);
+            } else {
+                panic!("Expected product delete command");
+            }
+        }
+
+        /// Tests that the CLI handles no command gracefully.
+        #[test]
+        fn test_parse_no_command() {
+            let args = vec!["cli"];
+
+            let cli = Cli::try_parse_from(args).unwrap();
+            
+            assert!(cli.command.is_none());
+        }
+
+        /// Tests that the CLI rejects invalid UUID format.
+        #[test]
+        fn test_parse_invalid_uuid() {
+            let args = vec![
+                "cli",
+                "user",
+                "get",
+                "--id", "invalid-uuid"
+            ];
+
+            let result = Cli::try_parse_from(args);
+            assert!(result.is_err());
+        }
+    }
+
+    mod user_commands {
+        use super::*;
+
+        /// Tests user creation command execution.
+        #[tokio::test]
+        async fn test_user_create_command() {
+            let cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::Create {
+                        username: "testuser".to_string(),
+                        email: "test@example.com".to_string(),
+                    }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            assert!(result.is_ok());
+        }
+
+        /// Tests user list command execution.
+        #[tokio::test]
+        async fn test_user_list_command() {
+            let cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::List
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            assert!(result.is_ok());
+        }
+
+        /// Tests user get command execution.
+        #[tokio::test]
+        async fn test_user_get_command() {
+            let user_id = Uuid::new_v4();
+            let cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::Get { id: user_id }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            // Should fail because user doesn't exist
+            assert!(result.is_err());
+        }
+
+        /// Tests user update command execution.
+        #[tokio::test]
+        async fn test_user_update_command() {
+            let user_id = Uuid::new_v4();
+            let cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::Update {
+                        id: user_id,
+                        username: Some("newuser".to_string()),
+                        email: Some("new@example.com".to_string()),
+                    }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            // Should fail because user doesn't exist
+            assert!(result.is_err());
+        }
+
+        /// Tests user delete command execution.
+        #[tokio::test]
+        async fn test_user_delete_command() {
+            let user_id = Uuid::new_v4();
+            let cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::Delete { id: user_id }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            // Should fail because user doesn't exist
+            assert!(result.is_err());
+        }
+    }
+
+    mod product_commands {
+        use super::*;
+
+        /// Tests product creation command execution.
+        #[tokio::test]
+        async fn test_product_create_command() {
+            let cli = Cli {
+                command: Some(Commands::Product {
+                    command: ProductCommands::Create {
+                        name: "Test Product".to_string(),
+                        description: "Test Description".to_string(),
+                    }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            assert!(result.is_ok());
+        }
+
+        /// Tests product list command execution.
+        #[tokio::test]
+        async fn test_product_list_command() {
+            let cli = Cli {
+                command: Some(Commands::Product {
+                    command: ProductCommands::List
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            assert!(result.is_ok());
+        }
+
+        /// Tests product get command execution.
+        #[tokio::test]
+        async fn test_product_get_command() {
+            let product_id = Uuid::new_v4();
+            let cli = Cli {
+                command: Some(Commands::Product {
+                    command: ProductCommands::Get { id: product_id }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            // Should fail because product doesn't exist
+            assert!(result.is_err());
+        }
+
+        /// Tests product update command execution.
+        #[tokio::test]
+        async fn test_product_update_command() {
+            let product_id = Uuid::new_v4();
+            let cli = Cli {
+                command: Some(Commands::Product {
+                    command: ProductCommands::Update {
+                        id: product_id,
+                        name: Some("New Product".to_string()),
+                        description: Some("New Description".to_string()),
+                    }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            // Should fail because product doesn't exist
+            assert!(result.is_err());
+        }
+
+        /// Tests product delete command execution.
+        #[tokio::test]
+        async fn test_product_delete_command() {
+            let product_id = Uuid::new_v4();
+            let cli = Cli {
+                command: Some(Commands::Product {
+                    command: ProductCommands::Delete { id: product_id }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            // Should fail because product doesn't exist
+            assert!(result.is_err());
+        }
+    }
+
+    mod integration_tests {
+        use super::*;
+
+        /// Tests complete user lifecycle through CLI commands.
+        #[tokio::test]
+        async fn test_user_lifecycle() {
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            // Create user
+            let create_cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::Create {
+                        username: "testuser".to_string(),
+                        email: "test@example.com".to_string(),
+                    }
+                })
+            };
+
+            let result = create_cli.run(user_service.clone(), product_service.clone()).await;
+            assert!(result.is_ok());
+
+            // Get the created user ID by listing users
+            let users = user_service.list().await.unwrap();
+            assert_eq!(users.len(), 1);
+            let user_id = users[0].id;
+
+            // Get user
+            let get_cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::Get { id: user_id }
+                })
+            };
+
+            let result = get_cli.run(user_service.clone(), product_service.clone()).await;
+            assert!(result.is_ok());
+
+            // Update user
+            let update_cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::Update {
+                        id: user_id,
+                        username: Some("updateduser".to_string()),
+                        email: None,
+                    }
+                })
+            };
+
+            let result = update_cli.run(user_service.clone(), product_service.clone()).await;
+            assert!(result.is_ok());
+
+            // Delete user
+            let delete_cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::Delete { id: user_id }
+                })
+            };
+
+            let result = delete_cli.run(user_service.clone(), product_service.clone()).await;
+            assert!(result.is_ok());
+
+            // Verify user is deleted
+            let users = user_service.list().await.unwrap();
+            assert_eq!(users.len(), 0);
+        }
+
+        /// Tests complete product lifecycle through CLI commands.
+        #[tokio::test]
+        async fn test_product_lifecycle() {
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            // Create product
+            let create_cli = Cli {
+                command: Some(Commands::Product {
+                    command: ProductCommands::Create {
+                        name: "Test Product".to_string(),
+                        description: "Test Description".to_string(),
+                    }
+                })
+            };
+
+            let result = create_cli.run(user_service.clone(), product_service.clone()).await;
+            assert!(result.is_ok());
+
+            // Get the created product ID by listing products
+            let products = product_service.list().await.unwrap();
+            assert_eq!(products.len(), 1);
+            let product_id = products[0].id;
+
+            // Get product
+            let get_cli = Cli {
+                command: Some(Commands::Product {
+                    command: ProductCommands::Get { id: product_id }
+                })
+            };
+
+            let result = get_cli.run(user_service.clone(), product_service.clone()).await;
+            assert!(result.is_ok());
+
+            // Update product
+            let update_cli = Cli {
+                command: Some(Commands::Product {
+                    command: ProductCommands::Update {
+                        id: product_id,
+                        name: Some("Updated Product".to_string()),
+                        description: None,
+                    }
+                })
+            };
+
+            let result = update_cli.run(user_service.clone(), product_service.clone()).await;
+            assert!(result.is_ok());
+
+            // Delete product
+            let delete_cli = Cli {
+                command: Some(Commands::Product {
+                    command: ProductCommands::Delete { id: product_id }
+                })
+            };
+
+            let result = delete_cli.run(user_service.clone(), product_service.clone()).await;
+            assert!(result.is_ok());
+
+            // Verify product is deleted
+            let products = product_service.list().await.unwrap();
+            assert_eq!(products.len(), 0);
+        }
+
+        /// Tests mixed user and product operations.
+        #[tokio::test]
+        async fn test_mixed_operations() {
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            // Create a user
+            let user_cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::Create {
+                        username: "testuser".to_string(),
+                        email: "test@example.com".to_string(),
+                    }
+                })
+            };
+
+            let result = user_cli.run(user_service.clone(), product_service.clone()).await;
+            assert!(result.is_ok());
+
+            // Create a product
+            let product_cli = Cli {
+                command: Some(Commands::Product {
+                    command: ProductCommands::Create {
+                        name: "Test Product".to_string(),
+                        description: "Test Description".to_string(),
+                    }
+                })
+            };
+
+            let result = product_cli.run(user_service.clone(), product_service.clone()).await;
+            assert!(result.is_ok());
+
+            // Verify both exist
+            let users = user_service.list().await.unwrap();
+            let products = product_service.list().await.unwrap();
+            assert_eq!(users.len(), 1);
+            assert_eq!(products.len(), 1);
+        }
+    }
+
+    mod error_handling {
+        use super::*;
+
+        /// Tests handling of service errors in user operations.
+        #[tokio::test]
+        async fn test_user_service_error() {
+            let cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::Get { id: Uuid::new_v4() }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            assert!(result.is_err());
+        }
+
+        /// Tests handling of service errors in product operations.
+        #[tokio::test]
+        async fn test_product_service_error() {
+            let cli = Cli {
+                command: Some(Commands::Product {
+                    command: ProductCommands::Get { id: Uuid::new_v4() }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            assert!(result.is_err());
+        }
+
+        /// Tests handling of no command provided.
+        #[tokio::test]
+        async fn test_no_command() {
+            let cli = Cli { command: None };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            assert!(result.is_ok());
+        }
+    }
+
+    mod edge_cases {
+        use super::*;
+
+        /// Tests CLI with empty strings in user creation.
+        #[tokio::test]
+        async fn test_user_create_empty_strings() {
+            let cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::Create {
+                        username: "".to_string(),
+                        email: "".to_string(),
+                    }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            assert!(result.is_ok()); // Should succeed even with empty strings
+        }
+
+        /// Tests CLI with empty strings in product creation.
+        #[tokio::test]
+        async fn test_product_create_empty_strings() {
+            let cli = Cli {
+                command: Some(Commands::Product {
+                    command: ProductCommands::Create {
+                        name: "".to_string(),
+                        description: "".to_string(),
+                    }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            assert!(result.is_ok()); // Should succeed even with empty strings
+        }
+
+        /// Tests CLI with very long strings.
+        #[tokio::test]
+        async fn test_user_create_long_strings() {
+            let long_username = "a".repeat(1000);
+            let long_email = format!("{}@example.com", "a".repeat(1000));
+            
+            let cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::Create {
+                        username: long_username.clone(),
+                        email: long_email.clone(),
+                    }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            assert!(result.is_ok());
+        }
+
+        /// Tests CLI with special characters in strings.
+        #[tokio::test]
+        async fn test_user_create_special_characters() {
+            let cli = Cli {
+                command: Some(Commands::User {
+                    command: UserCommands::Create {
+                        username: "user@#$%^&*()".to_string(),
+                        email: "test+tag@example.com".to_string(),
+                    }
+                })
+            };
+
+            let user_service = MockUserService::new();
+            let product_service = MockProductService::new();
+
+            let result = cli.run(user_service, product_service).await;
+            assert!(result.is_ok());
+        }
+    }
+}