🧪 ci: Add Tests for Custom Endpoint Header Resolution (#8045)

* Enhanced existing tests for the `resolveHeaders` function to cover all user field placeholders and messy scenarios.
* Added basic integration tests for custom endpoints initialization file

api/server/services/Endpoints/custom/initialize.spec.js

@@ -0,0 +1,93 @@
+const initializeClient = require('./initialize');
+
+jest.mock('@librechat/api', () => ({
+  resolveHeaders: jest.fn(),
+  getOpenAIConfig: jest.fn(),
+  createHandleLLMNewToken: jest.fn(),
+}));
+
+jest.mock('librechat-data-provider', () => ({
+  CacheKeys: { TOKEN_CONFIG: 'token_config' },
+  ErrorTypes: { NO_USER_KEY: 'NO_USER_KEY', NO_BASE_URL: 'NO_BASE_URL' },
+  envVarRegex: /\$\{([^}]+)\}/,
+  FetchTokenConfig: {},
+  extractEnvVariable: jest.fn((value) => value),
+}));
+
+jest.mock('@librechat/agents', () => ({
+  Providers: { OLLAMA: 'ollama' },
+}));
+
+jest.mock('~/server/services/UserService', () => ({
+  getUserKeyValues: jest.fn(),
+  checkUserKeyExpiry: jest.fn(),
+}));
+
+jest.mock('~/server/services/Config', () => ({
+  getCustomEndpointConfig: jest.fn().mockResolvedValue({
+    apiKey: 'test-key',
+    baseURL: 'https://test.com',
+    headers: { 'x-user': '{{LIBRECHAT_USER_ID}}', 'x-email': '{{LIBRECHAT_USER_EMAIL}}' },
+    models: { default: ['test-model'] },
+  }),
+}));
+
+jest.mock('~/server/services/ModelService', () => ({
+  fetchModels: jest.fn(),
+}));
+
+jest.mock('~/app/clients/OpenAIClient', () => {
+  return jest.fn().mockImplementation(() => ({
+    options: {},
+  }));
+});
+
+jest.mock('~/server/utils', () => ({
+  isUserProvided: jest.fn().mockReturnValue(false),
+}));
+
+jest.mock('~/cache/getLogStores', () =>
+  jest.fn().mockReturnValue({
+    get: jest.fn(),
+  }),
+);
+
+describe('custom/initializeClient', () => {
+  const mockRequest = {
+    body: { endpoint: 'test-endpoint' },
+    user: { id: 'user-123', email: 'test@example.com' },
+    app: { locals: {} },
+  };
+  const mockResponse = {};
+
+  beforeEach(() => {
+    jest.clearAllMocks();
+  });
+
+  it('calls resolveHeaders with headers and user', async () => {
+    const { resolveHeaders } = require('@librechat/api');
+    await initializeClient({ req: mockRequest, res: mockResponse, optionsOnly: true });
+    expect(resolveHeaders).toHaveBeenCalledWith(
+      { 'x-user': '{{LIBRECHAT_USER_ID}}', 'x-email': '{{LIBRECHAT_USER_EMAIL}}' },
+      { id: 'user-123', email: 'test@example.com' },
+    );
+  });
+
+  it('throws if endpoint config is missing', async () => {
+    const { getCustomEndpointConfig } = require('~/server/services/Config');
+    getCustomEndpointConfig.mockResolvedValueOnce(null);
+    await expect(
+      initializeClient({ req: mockRequest, res: mockResponse, optionsOnly: true }),
+    ).rejects.toThrow('Config not found for the test-endpoint custom endpoint.');
+  });
+
+  it('throws if user is missing', async () => {
+    await expect(
+      initializeClient({
+        req: { ...mockRequest, user: undefined },
+        res: mockResponse,
+        optionsOnly: true,
+      }),
+    ).rejects.toThrow("Cannot read properties of undefined (reading 'id')");
+  });
+});