Refactor command execution in bundler and gemset modules

This refactoring improves the architecture and testability of the Ruby
extension by introducing abstractions for command execution. Key changes:

- Add `CommandExecutor` trait for bundle commands with default impl
- Add `GemCommandExecutor` trait for gem commands with default impl
- Refactor Bundler and Gemset to accept executors via DI

The refactoring enables better testing through mock implementations while
keeping the original functionality intact.

Author: vitallium

src/bundler.rs

@@ -1,17 +1,67 @@
 use std::path::Path;
-use zed_extension_api::{Command, Result};
+use zed_extension_api::{process::Output, Command, Result};
+
+pub trait CommandExecutor {
+    fn execute_bundle(
+        &self,
+        sub_command: String,
+        args: Vec<String>,
+        envs: Vec<(String, String)>,
+        bundle_gemfile_path: &str,
+    ) -> Result<Output>;
+}
+
+pub struct RealCommandExecutor;
+
+impl CommandExecutor for RealCommandExecutor {
+    fn execute_bundle(
+        &self,
+        sub_command: String,
+        args: Vec<String>,
+        envs: Vec<(String, String)>,
+        bundle_gemfile_path: &str,
+    ) -> Result<Output> {
+        Command::new("bundle")
+            .arg(sub_command)
+            .args(args)
+            .envs(envs)
+            .env("BUNDLE_GEMFILE", bundle_gemfile_path)
+            .output()
+    }
+}
 
 /// A simple wrapper around the `bundle` command.
 pub struct Bundler {
     pub working_dir: String,
     envs: Vec<(String, String)>,
+    command_executor: Box<dyn CommandExecutor>,
 }
 
 impl Bundler {
-    pub fn new(working_dir: String, envs: Vec<(String, String)>) -> Self {
-        Bundler { working_dir, envs }
+    /// Creates a new `Bundler` instance.
+    ///
+    /// # Arguments
+    /// * `working_dir` - The working directory where `bundle` commands should be executed.
+    /// * `command_executor` - An executor for `bundle` commands.
+    pub fn new(
+        working_dir: String,
+        envs: Vec<(String, String)>,
+        command_executor: Box<dyn CommandExecutor>,
+    ) -> Self {
+        Bundler {
+            working_dir,
+            envs,
+            command_executor,
+        }
     }
 
+    /// Retrieves the installed version of a gem using `bundle info --version <name>`.
+    ///
+    /// # Arguments
+    /// * `name` - The name of the gem.
+    ///
+    /// # Returns
+    /// A `Result` containing the version string if successful, or an error message.
     pub fn installed_gem_version(&self, name: &str) -> Result<String> {
         let args = vec!["--version".into(), name.into()];
 
@@ -22,14 +72,10 @@ impl Bundler {
         let bundle_gemfile_path = Path::new(&self.working_dir).join("Gemfile");
         let bundle_gemfile = bundle_gemfile_path
             .to_str()
-            .ok_or("Invalid path to Gemfile")?;
+            .ok_or_else(|| "Invalid path to Gemfile".to_string())?;
 
-        Command::new("bundle")
-            .arg(cmd)
-            .args(args)
-            .envs(self.envs.clone())
-            .env("BUNDLE_GEMFILE", bundle_gemfile)
-            .output()
+        self.command_executor
+            .execute_bundle(cmd, args, self.envs.clone(), bundle_gemfile)
             .and_then(|output| match output.status {
                 Some(0) => Ok(String::from_utf8_lossy(&output.stdout).to_string()),
                 Some(status) => {
@@ -46,3 +92,178 @@ impl Bundler {
             })
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::cell::RefCell;
+
+    struct MockExecutorConfig {
+        output_to_return: Option<Result<Output>>,
+        expected_sub_command: Option<String>,
+        expected_args: Option<Vec<String>>,
+        expected_envs: Option<Vec<(String, String)>>,
+        expected_bundle_gemfile_path: Option<String>,
+    }
+
+    struct MockCommandExecutor {
+        config: RefCell<MockExecutorConfig>,
+    }
+
+    impl MockCommandExecutor {
+        fn new() -> Self {
+            MockCommandExecutor {
+                config: RefCell::new(MockExecutorConfig {
+                    output_to_return: None,
+                    expected_sub_command: None,
+                    expected_args: None,
+                    expected_envs: None,
+                    expected_bundle_gemfile_path: None,
+                }),
+            }
+        }
+
+        fn expect(
+            &self,
+            sub_command: &str,
+            args: &[&str],
+            envs: &[(&str, &str)],
+            bundle_gemfile_path: &str,
+            output: super::Result<Output>,
+        ) {
+            let mut config = self.config.borrow_mut();
+            config.expected_sub_command = Some(sub_command.to_string());
+            config.expected_args = Some(args.iter().map(|s| s.to_string()).collect());
+            config.expected_envs = Some(
+                envs.iter()
+                    .map(|&(k, v)| (k.to_string(), v.to_string()))
+                    .collect(),
+            );
+            config.expected_bundle_gemfile_path = Some(bundle_gemfile_path.to_string());
+            config.output_to_return = Some(output);
+        }
+    }
+
+    impl CommandExecutor for MockCommandExecutor {
+        fn execute_bundle(
+            &self,
+            sub_command: String,
+            args: Vec<String>,
+            envs: Vec<(String, String)>,
+            bundle_gemfile_path: &str,
+        ) -> super::Result<Output> {
+            let mut config = self.config.borrow_mut();
+
+            if let Some(expected_cmd) = &config.expected_sub_command {
+                assert_eq!(&sub_command, expected_cmd, "Mock: Sub-command mismatch");
+            }
+            if let Some(expected_args) = &config.expected_args {
+                assert_eq!(&args, expected_args, "Mock: Args mismatch");
+            }
+            if let Some(expected_envs) = &config.expected_envs {
+                assert_eq!(&envs, expected_envs, "Mock: Env mismatch");
+            }
+            if let Some(expected_path) = &config.expected_bundle_gemfile_path {
+                assert_eq!(
+                    bundle_gemfile_path, expected_path,
+                    "Mock: Gemfile path mismatch"
+                );
+            }
+
+            config.output_to_return.take().expect(
+                   "MockCommandExecutor: output_to_return was not set or already consumed for the test",
+               )
+        }
+    }
+
+    fn create_mock_executor_for_success(
+        version: &str,
+        dir: &str,
+        gem: &str,
+    ) -> MockCommandExecutor {
+        let mock = MockCommandExecutor::new();
+        mock.expect(
+            "info",
+            &["--version", gem],
+            &[],
+            &format!("{}/Gemfile", dir),
+            Ok(Output {
+                status: Some(0),
+                stdout: version.as_bytes().to_vec(),
+                stderr: Vec::new(),
+            }),
+        );
+        mock
+    }
+
+    #[test]
+    fn test_installed_gem_version_success() {
+        let mock_executor = create_mock_executor_for_success("8.0.0", "test_dir", "rails");
+        let bundler = Bundler::new("test_dir".into(), vec![], Box::new(mock_executor));
+        let version = bundler
+            .installed_gem_version("rails")
+            .expect("Expected successful version");
+        assert_eq!(version, "8.0.0", "Installed gem version should match");
+    }
+
+    #[test]
+    fn test_installed_gem_version_command_error() {
+        let mock_executor = MockCommandExecutor::new();
+        let gem_name = "unknown_gem";
+        let error_output = "Could not find gem 'unknown_gem'.";
+
+        mock_executor.expect(
+            "info",
+            &["--version", gem_name],
+            &[],
+            "test_dir/Gemfile",
+            Ok(Output {
+                status: Some(1),
+                stdout: Vec::new(),
+                stderr: error_output.as_bytes().to_vec(),
+            }),
+        );
+
+        let bundler = Bundler::new("test_dir".into(), vec![], Box::new(mock_executor));
+        let result = bundler.installed_gem_version(gem_name);
+
+        assert!(
+            result.is_err(),
+            "Expected error for failed gem version check"
+        );
+        let err_msg = result.unwrap_err();
+        assert!(
+            err_msg.contains("'bundle' command failed (status: 1)"),
+            "Error message should contain status"
+        );
+        assert!(
+            err_msg.contains(error_output),
+            "Error message should contain stderr output"
+        );
+    }
+
+    #[test]
+    fn test_installed_gem_version_execution_failure_from_executor() {
+        let mock_executor = MockCommandExecutor::new();
+        let gem_name = "critical_gem";
+        let specific_error_msg = "Mocked execution failure";
+
+        mock_executor.expect(
+            "info",
+            &["--version", gem_name],
+            &[],
+            "test_dir/Gemfile",
+            Err(specific_error_msg.to_string()),
+        );
+
+        let bundler = Bundler::new("test_dir".into(), vec![], Box::new(mock_executor));
+        let result = bundler.installed_gem_version(gem_name);
+
+        assert!(result.is_err(), "Expected error from executor failure");
+        assert_eq!(
+            result.unwrap_err(),
+            specific_error_msg,
+            "Error message should match executor error"
+        );
+    }
+}