refactor: improve resource dependency injection pattern

- Remove setTestExecutor/clearTestExecutor pattern from resources.ts
- Update resource handler to use standard default parameter pattern
- Simplify resource tests to match other test patterns in codebase
- Add documentation about dependency injection pattern in TESTING.md
- Ensure all handlers (tools, resources, future types) follow same DI pattern

This aligns resource implementation with established project patterns.

Author: cameroncooke

docs/TESTING.md

@@ -99,6 +99,13 @@ export default {
 };
 ```
 
+**Important**: The dependency injection pattern applies to ALL handlers, including:
+- Tool handlers
+- Resource handlers
+- Any future handler types (prompts, etc.)
+
+Always use default parameter values (e.g., `= getDefaultCommandExecutor()`) to ensure production code works without explicit executor injection, while tests can override with mock executors.
+
 ### Test Requirements
 
 All tests must explicitly provide mock executors:

src/core/__tests__/resources.test.ts

@@ -6,18 +6,13 @@ import {
   getAvailableResources,
   supportsResources,
   RESOURCE_URIS,
-  setTestExecutor,
-  clearTestExecutor,
 } from '../resources.js';
 import { createMockExecutor, CommandExecutor } from '../../utils/command.js';
 
 describe('resources', () => {
   let mockServer: McpServer;
 
   beforeEach(() => {
-    // Clear any test executor from previous tests
-    clearTestExecutor();
-
     // Create a mock MCP server using simple object structure
     mockServer = {
       resource: () => {},
@@ -118,9 +113,7 @@ describe('resources', () => {
         _uri: string,
         _description: string,
         _options: { mimeType: string },
-        handler: (
-          executor?: CommandExecutor,
-        ) => Promise<{ contents: Array<{ type: 'text'; text: string }> }>,
+        handler: any,
       ) => {
         resourceHandler = handler;
       };

src/core/resources.ts

@@ -16,12 +16,6 @@ import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
 import { log, getDefaultCommandExecutor, CommandExecutor } from '../utils/index.js';
 import { list_simsLogic } from '../plugins/simulator-shared/list_sims.js';
 
-/**
- * Test executor injection for dependency injection during testing
- * This allows tests to override the executor without modifying production code
- */
-let testExecutor: CommandExecutor | undefined;
-
 /**
  * Resource URI schemes supported by XcodeBuildMCP
  */
@@ -39,34 +33,20 @@ export function supportsResources(): boolean {
   return true;
 }
 
-/**
- * Set test executor for dependency injection (testing only)
- * @param executor Test executor to use
- */
-export function setTestExecutor(executor: CommandExecutor): void {
-  testExecutor = executor;
-}
-
-/**
- * Clear test executor (testing only)
- */
-export function clearTestExecutor(): void {
-  testExecutor = undefined;
-}
-
 /**
  * Resource handler for simulator data
  * Uses existing list_simsLogic to maintain consistency
+ * @param executor Optional command executor for dependency injection
  */
-async function handleSimulatorsResource(executor?: CommandExecutor): Promise<{
+async function handleSimulatorsResource(
+  executor: CommandExecutor = getDefaultCommandExecutor(),
+): Promise<{
   contents: Array<{ type: 'text'; text: string }>;
 }> {
   try {
     log('info', 'Processing simulators resource request');
 
-    // Use provided executor, or test executor, or default executor (in that order)
-    const effectiveExecutor = executor || testExecutor || getDefaultCommandExecutor();
-    const result = await list_simsLogic({}, effectiveExecutor);
+    const result = await list_simsLogic({}, executor);
 
     if (result.isError) {
       throw new Error(result.content[0]?.text || 'Failed to retrieve simulator data');
@@ -102,13 +82,12 @@ async function handleSimulatorsResource(executor?: CommandExecutor): Promise<{
 export function registerResources(server: McpServer): void {
   log('info', 'Registering MCP resources');
 
-  // Register simulators resource with wrapper that supports test executor injection
-  // The wrapper allows tests to pass an executor parameter for dependency injection
+  // Register simulators resource
   server.resource(
     RESOURCE_URIS.SIMULATORS,
     'Available iOS simulators with their UUIDs and states',
     { mimeType: 'text/plain' },
-    (executor?: CommandExecutor) => handleSimulatorsResource(executor),
+    handleSimulatorsResource,
   );
 
   log('info', `Registered resource: ${RESOURCE_URIS.SIMULATORS}`);