Add comprehensive tests for strategy pattern and verify implementation

Co-authored-by: oleander <220827+oleander@users.noreply.github.com>

Author: Copilot

tests/fallback_strategy_test.rs

@@ -0,0 +1,99 @@
+use ai::generation::fallback::{generate_with_fallback, get_api_key, validate_api_key};
+use ai::config::AppConfig;
+
+#[tokio::test]
+async fn test_fallback_strategy_no_api_key() {
+    // Clear environment to ensure clean test
+    std::env::remove_var("OPENAI_API_KEY");
+    
+    let test_diff = r#"diff --git a/src/auth.rs b/src/auth.rs
+new file mode 100644
+index 0000000..1234567
+--- /dev/null
++++ b/src/auth.rs
+@@ -0,0 +1,5 @@
++pub fn authenticate(user: &str, pass: &str) -> bool {
++    user == "admin" && pass == "secret"
++}
+"#;
+
+    let mut config = AppConfig::default();
+    config.openai_api_key = None;
+    
+    let result = generate_with_fallback(test_diff, &config).await;
+    
+    // Should succeed with local generation
+    assert!(result.is_ok(), "Expected fallback to succeed, got: {:?}", result.err());
+    
+    let message = result.unwrap();
+    assert!(!message.is_empty(), "Generated message should not be empty");
+    assert!(message.len() <= 72, "Message should respect default length limit"); // Default max_commit_length
+}
+
+#[tokio::test] 
+async fn test_fallback_strategy_invalid_api_key() {
+    let test_diff = r#"diff --git a/src/test.py b/src/test.py
+new file mode 100644
+index 0000000..abc123
+--- /dev/null
++++ b/src/test.py
+@@ -0,0 +1,3 @@
++def hello():
++    return "Hello, World!"
+"#;
+
+    let mut config = AppConfig::default();
+    config.openai_api_key = Some("<PLACE HOLDER FOR YOUR API KEY>".to_string());
+    
+    let result = generate_with_fallback(test_diff, &config).await;
+    
+    // Should succeed with local fallback
+    assert!(result.is_ok(), "Expected fallback to succeed, got: {:?}", result.err());
+    
+    let message = result.unwrap();
+    assert!(!message.is_empty(), "Generated message should not be empty");
+}
+
+#[test]
+fn test_api_key_validation() {
+    // Test various invalid keys
+    assert!(validate_api_key(None).is_err());
+    assert!(validate_api_key(Some("")).is_err());
+    assert!(validate_api_key(Some("<PLACE HOLDER FOR YOUR API KEY>")).is_err());
+    
+    // Test valid key
+    assert!(validate_api_key(Some("sk-valid-key-123")).is_ok());
+}
+
+#[test]
+fn test_get_api_key_from_config() {
+    // Test with valid config
+    let mut config = AppConfig::default();
+    config.openai_api_key = Some("test-key-123".to_string());
+    assert!(get_api_key(&config).is_ok());
+    
+    // Test with invalid config
+    config.openai_api_key = Some("<PLACE HOLDER FOR YOUR API KEY>".to_string());
+    assert!(get_api_key(&config).is_err());
+    
+    // Test with no config
+    config.openai_api_key = None;
+    std::env::remove_var("OPENAI_API_KEY");
+    assert!(get_api_key(&config).is_err());
+}
+
+#[test]
+fn test_get_api_key_from_env() {
+    // Set environment variable
+    std::env::set_var("OPENAI_API_KEY", "env-test-key");
+    
+    let mut config = AppConfig::default();
+    config.openai_api_key = None;
+    
+    let result = get_api_key(&config);
+    assert!(result.is_ok());
+    assert_eq!(result.unwrap(), "env-test-key");
+    
+    // Clean up
+    std::env::remove_var("OPENAI_API_KEY");
+}