diff --git a/server/src/llm/chat.rs b/server/src/llm/chat.rs
index 7a2a69b..c951fff 100644
--- a/server/src/llm/chat.rs
+++ b/server/src/llm/chat.rs
@@ -22,6 +22,7 @@ pub struct ProviderConfig {
 
 /// Result of a chat call, including messages and optional metadata.
 #[allow(dead_code)]
+#[derive(Debug)]
 pub struct ChatResult {
     pub messages: Vec<Message>,
     /// Session ID returned by Claude Code for resumption.
@@ -451,3 +452,547 @@ pub fn cancel_chat(state: &SessionState) -> Result<(), String> {
     state.cancel_tx.send(true).map_err(|e| e.to_string())?;
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::llm::types::{FunctionCall, ToolCall};
+    use crate::state::SessionState;
+    use serde_json::json;
+    use std::collections::HashMap;
+    use std::sync::Mutex;
+
+    // ---------------------------------------------------------------------------
+    // Minimal in-memory StoreOps mock
+    // ---------------------------------------------------------------------------
+
+    struct MockStore {
+        data: Mutex<HashMap<String, serde_json::Value>>,
+        save_should_fail: bool,
+    }
+
+    impl MockStore {
+        fn new() -> Self {
+            Self {
+                data: Mutex::new(HashMap::new()),
+                save_should_fail: false,
+            }
+        }
+
+        fn with_save_error() -> Self {
+            Self {
+                data: Mutex::new(HashMap::new()),
+                save_should_fail: true,
+            }
+        }
+
+        fn with_entry(key: &str, value: serde_json::Value) -> Self {
+            let mut map = HashMap::new();
+            map.insert(key.to_string(), value);
+            Self {
+                data: Mutex::new(map),
+                save_should_fail: false,
+            }
+        }
+    }
+
+    impl StoreOps for MockStore {
+        fn get(&self, key: &str) -> Option<serde_json::Value> {
+            self.data.lock().ok().and_then(|m| m.get(key).cloned())
+        }
+
+        fn set(&self, key: &str, value: serde_json::Value) {
+            if let Ok(mut m) = self.data.lock() {
+                m.insert(key.to_string(), value);
+            }
+        }
+
+        fn delete(&self, key: &str) {
+            if let Ok(mut m) = self.data.lock() {
+                m.remove(key);
+            }
+        }
+
+        fn save(&self) -> Result<(), String> {
+            if self.save_should_fail {
+                Err("mock save error".to_string())
+            } else {
+                Ok(())
+            }
+        }
+    }
+
+    // ---------------------------------------------------------------------------
+    // parse_tool_arguments
+    // ---------------------------------------------------------------------------
+
+    #[test]
+    fn parse_tool_arguments_valid_json() {
+        let result = parse_tool_arguments(r#"{"path": "src/main.rs"}"#);
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap()["path"], json!("src/main.rs"));
+    }
+
+    #[test]
+    fn parse_tool_arguments_invalid_json() {
+        let result = parse_tool_arguments("not json {{{");
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("Error parsing arguments:"));
+    }
+
+    #[test]
+    fn parse_tool_arguments_empty_object() {
+        let result = parse_tool_arguments("{}");
+        assert!(result.is_ok());
+    }
+
+    // ---------------------------------------------------------------------------
+    // get_anthropic_api_key_exists_impl
+    // ---------------------------------------------------------------------------
+
+    #[test]
+    fn api_key_exists_when_key_is_present_and_non_empty() {
+        let store = MockStore::with_entry("anthropic_api_key", json!("sk-test-key"));
+        assert!(get_anthropic_api_key_exists_impl(&store));
+    }
+
+    #[test]
+    fn api_key_exists_returns_false_when_key_is_empty_string() {
+        let store = MockStore::with_entry("anthropic_api_key", json!(""));
+        assert!(!get_anthropic_api_key_exists_impl(&store));
+    }
+
+    #[test]
+    fn api_key_exists_returns_false_when_key_absent() {
+        let store = MockStore::new();
+        assert!(!get_anthropic_api_key_exists_impl(&store));
+    }
+
+    #[test]
+    fn api_key_exists_returns_false_when_value_is_not_string() {
+        let store = MockStore::with_entry("anthropic_api_key", json!(42));
+        assert!(!get_anthropic_api_key_exists_impl(&store));
+    }
+
+    // ---------------------------------------------------------------------------
+    // get_anthropic_api_key_impl
+    // ---------------------------------------------------------------------------
+
+    #[test]
+    fn get_api_key_returns_key_when_present() {
+        let store = MockStore::with_entry("anthropic_api_key", json!("sk-test-key"));
+        let result = get_anthropic_api_key_impl(&store);
+        assert_eq!(result.unwrap(), "sk-test-key");
+    }
+
+    #[test]
+    fn get_api_key_errors_when_empty() {
+        let store = MockStore::with_entry("anthropic_api_key", json!(""));
+        let result = get_anthropic_api_key_impl(&store);
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("empty"));
+    }
+
+    #[test]
+    fn get_api_key_errors_when_absent() {
+        let store = MockStore::new();
+        let result = get_anthropic_api_key_impl(&store);
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("not found"));
+    }
+
+    #[test]
+    fn get_api_key_errors_when_value_not_string() {
+        let store = MockStore::with_entry("anthropic_api_key", json!(123));
+        let result = get_anthropic_api_key_impl(&store);
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("not a string"));
+    }
+
+    // ---------------------------------------------------------------------------
+    // set_anthropic_api_key_impl
+    // ---------------------------------------------------------------------------
+
+    #[test]
+    fn set_api_key_stores_and_returns_ok() {
+        let store = MockStore::new();
+        let result = set_anthropic_api_key_impl(&store, "sk-my-key");
+        assert!(result.is_ok());
+        assert_eq!(
+            store.get("anthropic_api_key"),
+            Some(json!("sk-my-key"))
+        );
+    }
+
+    #[test]
+    fn set_api_key_returns_error_when_save_fails() {
+        let store = MockStore::with_save_error();
+        let result = set_anthropic_api_key_impl(&store, "sk-my-key");
+        assert!(result.is_err());
+        assert!(result.unwrap_err().contains("mock save error"));
+    }
+
+    // ---------------------------------------------------------------------------
+    // Public wrappers: get_anthropic_api_key_exists / set_anthropic_api_key
+    // ---------------------------------------------------------------------------
+
+    #[test]
+    fn public_api_key_exists_returns_ok_bool() {
+        let store = MockStore::with_entry("anthropic_api_key", json!("sk-abc"));
+        let result = get_anthropic_api_key_exists(&store);
+        assert_eq!(result, Ok(true));
+    }
+
+    #[test]
+    fn public_api_key_exists_false_when_absent() {
+        let store = MockStore::new();
+        let result = get_anthropic_api_key_exists(&store);
+        assert_eq!(result, Ok(false));
+    }
+
+    #[test]
+    fn public_set_api_key_succeeds() {
+        let store = MockStore::new();
+        let result = set_anthropic_api_key(&store, "sk-xyz".to_string());
+        assert!(result.is_ok());
+    }
+
+    #[test]
+    fn public_set_api_key_propagates_save_error() {
+        let store = MockStore::with_save_error();
+        let result = set_anthropic_api_key(&store, "sk-xyz".to_string());
+        assert!(result.is_err());
+    }
+
+    // ---------------------------------------------------------------------------
+    // get_tool_definitions
+    // ---------------------------------------------------------------------------
+
+    #[test]
+    fn tool_definitions_returns_five_tools() {
+        let tools = get_tool_definitions();
+        assert_eq!(tools.len(), 5);
+    }
+
+    #[test]
+    fn tool_definitions_has_expected_names() {
+        let tools = get_tool_definitions();
+        let names: Vec<&str> = tools.iter().map(|t| t.function.name.as_str()).collect();
+        assert!(names.contains(&"read_file"));
+        assert!(names.contains(&"write_file"));
+        assert!(names.contains(&"list_directory"));
+        assert!(names.contains(&"search_files"));
+        assert!(names.contains(&"exec_shell"));
+    }
+
+    #[test]
+    fn tool_definitions_each_has_function_kind() {
+        let tools = get_tool_definitions();
+        for tool in &tools {
+            assert_eq!(tool.kind, "function");
+        }
+    }
+
+    #[test]
+    fn tool_definitions_each_has_non_empty_description() {
+        let tools = get_tool_definitions();
+        for tool in &tools {
+            assert!(!tool.function.description.is_empty());
+        }
+    }
+
+    #[test]
+    fn tool_definitions_parameters_have_object_type() {
+        let tools = get_tool_definitions();
+        for tool in &tools {
+            assert_eq!(tool.function.parameters["type"], json!("object"));
+        }
+    }
+
+    #[test]
+    fn read_file_tool_requires_path_parameter() {
+        let tools = get_tool_definitions();
+        let read_file = tools
+            .iter()
+            .find(|t| t.function.name == "read_file")
+            .unwrap();
+        let required = read_file.function.parameters["required"]
+            .as_array()
+            .unwrap();
+        let required_names: Vec<&str> =
+            required.iter().map(|v| v.as_str().unwrap()).collect();
+        assert!(required_names.contains(&"path"));
+    }
+
+    #[test]
+    fn exec_shell_tool_requires_command_and_args() {
+        let tools = get_tool_definitions();
+        let exec_shell = tools
+            .iter()
+            .find(|t| t.function.name == "exec_shell")
+            .unwrap();
+        let required = exec_shell.function.parameters["required"]
+            .as_array()
+            .unwrap();
+        let required_names: Vec<&str> =
+            required.iter().map(|v| v.as_str().unwrap()).collect();
+        assert!(required_names.contains(&"command"));
+        assert!(required_names.contains(&"args"));
+    }
+
+    // ---------------------------------------------------------------------------
+    // cancel_chat
+    // ---------------------------------------------------------------------------
+
+    #[test]
+    fn cancel_chat_sends_true_to_channel() {
+        let state = SessionState::default();
+        let result = cancel_chat(&state);
+        assert!(result.is_ok());
+        assert!(*state.cancel_rx.borrow());
+    }
+
+    // ---------------------------------------------------------------------------
+    // chat — unsupported provider early return (no network calls)
+    // ---------------------------------------------------------------------------
+
+    #[tokio::test]
+    async fn chat_rejects_unknown_provider() {
+        let state = SessionState::default();
+        let store = MockStore::new();
+        let config = ProviderConfig {
+            provider: "unsupported-provider".to_string(),
+            model: "some-model".to_string(),
+            base_url: None,
+            enable_tools: None,
+            session_id: None,
+        };
+        let messages = vec![Message {
+            role: Role::User,
+            content: "hello".to_string(),
+            tool_calls: None,
+            tool_call_id: None,
+        }];
+
+        let result = chat(
+            messages,
+            config,
+            &state,
+            &store,
+            |_| {},
+            |_| {},
+            |_| {},
+        )
+        .await;
+
+        assert!(result.is_err());
+        assert!(result
+            .unwrap_err()
+            .contains("Unsupported provider: unsupported-provider"));
+    }
+
+    // ---------------------------------------------------------------------------
+    // chat — ollama path exercises system prompt insertion + tool setup
+    //         (connection to a non-existent port fails fast)
+    // ---------------------------------------------------------------------------
+
+    #[tokio::test]
+    async fn chat_ollama_bad_url_fails_with_ollama_error() {
+        let state = SessionState::default();
+        let store = MockStore::new();
+        let config = ProviderConfig {
+            provider: "ollama".to_string(),
+            model: "llama3".to_string(),
+            // Port 1 is reserved / closed — connection fails immediately.
+            base_url: Some("http://127.0.0.1:1".to_string()),
+            enable_tools: Some(false),
+            session_id: None,
+        };
+        let messages = vec![Message {
+            role: Role::User,
+            content: "ping".to_string(),
+            tool_calls: None,
+            tool_call_id: None,
+        }];
+
+        let result = chat(
+            messages,
+            config,
+            &state,
+            &store,
+            |_| {},
+            |_| {},
+            |_| {},
+        )
+        .await;
+
+        assert!(result.is_err());
+        let err = result.unwrap_err();
+        assert!(err.contains("Ollama Error:"), "unexpected error: {err}");
+    }
+
+    // ---------------------------------------------------------------------------
+    // chat — Anthropic model prefix detection (fails without API key)
+    // ---------------------------------------------------------------------------
+
+    #[tokio::test]
+    async fn chat_claude_model_without_api_key_returns_error() {
+        let state = SessionState::default();
+        // No API key in store → should fail with "API key not found"
+        let store = MockStore::new();
+        let config = ProviderConfig {
+            provider: "anthropic".to_string(),
+            model: "claude-3-haiku-20240307".to_string(),
+            base_url: None,
+            enable_tools: Some(false),
+            session_id: None,
+        };
+        let messages = vec![Message {
+            role: Role::User,
+            content: "hello".to_string(),
+            tool_calls: None,
+            tool_call_id: None,
+        }];
+
+        let result = chat(
+            messages,
+            config,
+            &state,
+            &store,
+            |_| {},
+            |_| {},
+            |_| {},
+        )
+        .await;
+
+        assert!(result.is_err());
+        let err = result.unwrap_err();
+        assert!(
+            err.contains("API key"),
+            "expected API key error, got: {err}"
+        );
+    }
+
+    // ---------------------------------------------------------------------------
+    // execute_tool — unknown tool name (no I/O, no network)
+    // ---------------------------------------------------------------------------
+
+    #[tokio::test]
+    async fn execute_tool_returns_error_for_unknown_tool() {
+        let state = SessionState::default();
+        let call = ToolCall {
+            id: Some("call-1".to_string()),
+            kind: "function".to_string(),
+            function: FunctionCall {
+                name: "nonexistent_tool".to_string(),
+                arguments: "{}".to_string(),
+            },
+        };
+
+        let result = execute_tool(&call, &state).await;
+        assert_eq!(result, "Unknown tool: nonexistent_tool");
+    }
+
+    #[tokio::test]
+    async fn execute_tool_returns_parse_error_for_invalid_json_args() {
+        let state = SessionState::default();
+        let call = ToolCall {
+            id: Some("call-2".to_string()),
+            kind: "function".to_string(),
+            function: FunctionCall {
+                name: "read_file".to_string(),
+                arguments: "INVALID JSON".to_string(),
+            },
+        };
+
+        let result = execute_tool(&call, &state).await;
+        assert!(
+            result.contains("Error parsing arguments:"),
+            "unexpected result: {result}"
+        );
+    }
+
+    // ---------------------------------------------------------------------------
+    // execute_tool — tools that use SessionState (no project root → errors)
+    // ---------------------------------------------------------------------------
+
+    #[tokio::test]
+    async fn execute_tool_read_file_no_project_root_returns_error() {
+        let state = SessionState::default(); // no project_root set
+        let call = ToolCall {
+            id: None,
+            kind: "function".to_string(),
+            function: FunctionCall {
+                name: "read_file".to_string(),
+                arguments: r#"{"path": "some_file.txt"}"#.to_string(),
+            },
+        };
+
+        let result = execute_tool(&call, &state).await;
+        assert!(result.starts_with("Error:"), "unexpected result: {result}");
+    }
+
+    #[tokio::test]
+    async fn execute_tool_write_file_no_project_root_returns_error() {
+        let state = SessionState::default();
+        let call = ToolCall {
+            id: None,
+            kind: "function".to_string(),
+            function: FunctionCall {
+                name: "write_file".to_string(),
+                arguments: r#"{"path": "out.txt", "content": "hello"}"#.to_string(),
+            },
+        };
+
+        let result = execute_tool(&call, &state).await;
+        assert!(result.starts_with("Error:"), "unexpected result: {result}");
+    }
+
+    #[tokio::test]
+    async fn execute_tool_list_directory_no_project_root_returns_error() {
+        let state = SessionState::default();
+        let call = ToolCall {
+            id: None,
+            kind: "function".to_string(),
+            function: FunctionCall {
+                name: "list_directory".to_string(),
+                arguments: r#"{"path": "."}"#.to_string(),
+            },
+        };
+
+        let result = execute_tool(&call, &state).await;
+        assert!(result.starts_with("Error:"), "unexpected result: {result}");
+    }
+
+    #[tokio::test]
+    async fn execute_tool_search_files_no_project_root_returns_error() {
+        let state = SessionState::default();
+        let call = ToolCall {
+            id: None,
+            kind: "function".to_string(),
+            function: FunctionCall {
+                name: "search_files".to_string(),
+                arguments: r#"{"query": "fn main"}"#.to_string(),
+            },
+        };
+
+        let result = execute_tool(&call, &state).await;
+        assert!(result.starts_with("Error:"), "unexpected result: {result}");
+    }
+
+    #[tokio::test]
+    async fn execute_tool_exec_shell_no_project_root_returns_error() {
+        let state = SessionState::default();
+        let call = ToolCall {
+            id: None,
+            kind: "function".to_string(),
+            function: FunctionCall {
+                name: "exec_shell".to_string(),
+                arguments: r#"{"command": "ls", "args": []}"#.to_string(),
+            },
+        };
+
+        let result = execute_tool(&call, &state).await;
+        assert!(result.starts_with("Error:"), "unexpected result: {result}");
+    }
+}