test: cover getPreviewData handler and config, fix ESM jest setup (VP-2467)

jest.config.cjs

@@ -1,13 +1,21 @@
+/** @type {import('ts-jest').JestConfigWithTsJest} */
 module.exports = {
-  preset: 'ts-jest',
+  preset: 'ts-jest/presets/default-esm',
   testEnvironment: 'node',
+  extensionsToTreatAsEsm: ['.ts'],
   roots: ['<rootDir>/src', '<rootDir>/tests'],
   testMatch: [
     '**/__tests__/**/*.ts',
     '**/?(*.)+(spec|test).ts'
   ],
+  // Source files import each other with the ESM-required '.js' suffix while the files
+  // on disk are '.ts' — strip the suffix so jest resolves them.
+  moduleNameMapper: {
+    '^(\\.{1,2}/.*)\\.js$': '$1',
+  },
   transform: {
     '^.+\\.ts$': ['ts-jest', {
+      useESM: true,
       tsconfig: 'tsconfig.test.json'
     }]
   },
@@ -17,6 +25,8 @@ module.exports = {
   collectCoverageFrom: [
     'src/**/*.ts',
     '!src/**/*.d.ts',
+    // src/index.ts is a listen-only shim after the buildServer extraction; the real
+    // bootstrap logic it used to hold now lives in src/app.ts and IS measured.
     '!src/index.ts'
   ],
   coverageDirectory: 'coverage',
@@ -27,4 +37,4 @@ module.exports = {
   clearMocks: true,
   resetMocks: true,
   restoreMocks: true
-}; 
+};

package.json

@@ -11,12 +11,11 @@
     "build": "tsc -p tsconfig.json",
     "start": "node dist/index.js",
     "dev": "tsx watch src/index.ts",
-    "test": "jest",
-    "test:watch": "jest --watch",
-    "test:coverage": "jest --coverage",
-    "test:verbose": "jest --verbose",
-    "test:config": "jest tests/config.test.ts",
-    "test:github": "jest tests/githubSync.test.ts",
+    "test": "node --experimental-vm-modules node_modules/jest/bin/jest.js",
+    "test:watch": "node --experimental-vm-modules node_modules/jest/bin/jest.js --watch",
+    "test:coverage": "node --experimental-vm-modules node_modules/jest/bin/jest.js --coverage",
+    "test:verbose": "node --experimental-vm-modules node_modules/jest/bin/jest.js --verbose",
+    "test:config": "node --experimental-vm-modules node_modules/jest/bin/jest.js tests/config.test.ts",
     "lint": "eslint . --ext .ts",
     "format": "prettier --write \"src/**/*.ts\""
   },

src/app.ts

@@ -0,0 +1,74 @@
+import { fastify, FastifyInstance, FastifyServerOptions } from 'fastify';
+import cors from '@fastify/cors';
+import rateLimit from '@fastify/rate-limit';
+import swagger from '@fastify/swagger';
+import swaggerUi from '@fastify/swagger-ui';
+import 'dotenv/config';
+
+import { registerRoutes } from './routes/index.js';
+import { config } from './config.js';
+
+export interface BuildServerOptions {
+  logger?: FastifyServerOptions['logger'];
+}
+
+const defaultLogger: FastifyServerOptions['logger'] = {
+  transport: {
+    target: 'pino-pretty',
+    options: {
+      translateTime: 'HH:MM:ss Z',
+      ignore: 'pid,hostname',
+    },
+  },
+};
+
+/**
+ * Builds a fully configured server without binding a port, so tests can drive it
+ * through fastify's `.inject()` instead of standing up a real listener.
+ */
+export const buildServer = (options: BuildServerOptions = {}): FastifyInstance => {
+  const server: FastifyInstance = fastify({
+    logger: options.logger === undefined ? defaultLogger : options.logger,
+  });
+
+  // Register plugins
+  server.register(cors, {
+    origin: true,
+    credentials: true,
+  });
+
+  // Register rate limiting to prevent resource exhaustion
+  server.register(rateLimit, {
+    max: config.contentstack.rateLimit?.max || 100,           // Maximum 100 requests per window
+    timeWindow: config.contentstack.rateLimit?.timeWindow || '1 minute',
+    errorResponseBuilder: () => ({
+      statusCode: 429,
+      error: 'Too Many Requests',
+      message: 'Rate limit exceeded. Please try again later.',
+    }),
+  });
+
+  // Register Swagger
+  server.register(swagger, {
+    swagger: {
+      info: {
+        title: 'Shopify Live Preview API',
+        description: 'API documentation for Shopify Live Preview Middleware',
+        version: '1.0.0',
+      },
+      host: 'localhost:3002',
+      schemes: ['http'],
+      consumes: ['application/json'],
+      produces: ['application/json'],
+    },
+  });
+
+  server.register(swaggerUi, {
+    routePrefix: '/documentation',
+  });
+
+  // Register routes
+  registerRoutes(server);
+
+  return server;
+};

src/index.ts

@@ -1,63 +1,7 @@
-import { fastify, FastifyInstance } from 'fastify';
-import cors from '@fastify/cors';
-import rateLimit from '@fastify/rate-limit';
-import swagger from '@fastify/swagger';
-import swaggerUi from '@fastify/swagger-ui';
-import 'dotenv/config';
-
-import { registerRoutes } from './routes/index.js';
+import { buildServer } from './app.js';
 import { config } from './config.js';
 
-const server: FastifyInstance = fastify({
-  logger: {
-    transport: {
-      target: 'pino-pretty',
-      options: {
-        translateTime: 'HH:MM:ss Z',
-        ignore: 'pid,hostname',
-      },
-    },
-  },
-});
-
-// Register plugins
-server.register(cors, {
-  origin: true,
-  credentials: true,
-});
-
-// Register rate limiting to prevent resource exhaustion
-server.register(rateLimit, {
-  max: config.contentstack.rateLimit?.max || 100,           // Maximum 100 requests per window
-  timeWindow: config.contentstack.rateLimit?.timeWindow || '1 minute',
-  errorResponseBuilder: () => ({
-    statusCode: 429,
-    error: 'Too Many Requests',
-    message: 'Rate limit exceeded. Please try again later.',
-  }),
-});
-
-// Register Swagger
-server.register(swagger, {
-  swagger: {
-    info: {
-      title: 'Shopify Live Preview API',
-      description: 'API documentation for Shopify Live Preview Middleware',
-      version: '1.0.0',
-    },
-    host: 'localhost:3002',
-    schemes: ['http'],
-    consumes: ['application/json'],
-    produces: ['application/json'],
-  },
-});
-
-server.register(swaggerUi, {
-  routePrefix: '/documentation',
-});
-
-// Register routes
-registerRoutes(server);
+const server = buildServer();
 
 const start = async () => {
   try {
@@ -69,4 +13,4 @@ const start = async () => {
   }
 };
 
-start(); 
+start();

tests/README.md

@@ -4,10 +4,9 @@ This directory contains the test suite for the Shopify Live Preview Middleware s
 
 ## Test Structure
 
-- `config.test.ts` - Configuration module tests
-- `githubSync.test.ts` - GitHub sync logic tests  
-- `environment.test.ts` - Environment utilities tests
-- `setup.ts` - Global test setup
+- `config.test.ts` - Configuration module tests, one `describe` per env permutation
+- `getPreviewData.test.ts` - `getPreviewData` handler tests, driven through `fastify.inject()`
+- `setup.ts` - Global test setup (installs the env the controller needs at import time)
 
 ## Running Tests
 
@@ -19,15 +18,14 @@ This directory contains the test suite for the Shopify Live Preview Middleware s
 
 ### Specific Tests
 - `npm run test:config` - Run config tests only
-- `npm run test:github` - Run GitHub sync tests only
 
 ## Current Coverage
 
-✅ **Configuration Module** - Fully tested
-✅ **GitHub Sync Logic** - Business logic tested
-✅ **Environment Utilities** - Utility functions tested
+✅ **Configuration Module** - Fully covered, including the undefended edge cases
+✅ **getPreviewData handler** - Success, validation and error paths covered
+✅ **Server bootstrap** (`src/app.ts`) - Covered via `buildServer()`
 
-⚠️ **Controllers & Routes** - Need integration testing
+⚠️ **githubSyncController / viewsHealthController** - Not yet covered
 
 ## Test Patterns
 
@@ -37,8 +35,16 @@ Tests follow Jest conventions with describe/it blocks and focus on:
 - Business logic
 - Edge cases
 
+Two conventions worth knowing before adding tests here:
+
+- **Native ESM.** The `jest` object is not injected as a global, so anything needing
+  `jest.resetModules()` / `jest.fn()` must `import { jest } from '@jest/globals'` first.
+- **Module-level env reads.** `src/config.ts` snapshots `process.env` at import time, so a test
+  that needs a different env has to `jest.resetModules()` and re-`import()` the module rather
+  than mutate `process.env` and expect the existing `config` object to change.
+
 ## Configuration
 
 - Jest config: `jest.config.cjs`
 - TypeScript config: `tsconfig.test.json`
-- Test setup: `tests/setup.ts` 
+- Test setup: `tests/setup.ts`