jest: own the transform pipeline — next/jest force-ignores /node_modules/ even…

jest: own the transform pipeline — next/jest force-ignores /node_modules/ even in PnP cache paths, so ESM deps shipped untransformed and the whole suite never ran
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

jest.config.js

-const nextJest = require('next/jest');
-
 /**
- * Jest config for the Next.js app (root: next/).
- * Uses next/jest SWC transformer and jsdom environment.
+ * Jest config for the Next.js app.
  * Yarn PnP compatible via jest-pnp-resolver.
+ *
+ * Why not next/jest: its config factory hard-prepends `/node_modules/` to
+ * transformIgnorePatterns ("custom config can append but not modify it").
+ * Under Yarn PnP every dependency resolves into a cache path shaped
+ * `…/<pkg>.zip/node_modules/<pkg>/…`, so the pattern matches ALL deps and the
+ * ESM-only unified markdown chain (unified, remark-*, shiki…) is shipped
+ * untransformed to the CJS runtime, which cannot parse `export`. We keep the
+ * same SWC transformer next/jest uses, plus the same CSS/image/font mocks,
+ * but own the ignore list: only CSS modules are excluded, so dependencies in
+ * the PnP cache get transformed like source files.
  */
-const createJestConfig = nextJest({
-  dir: './',
-});
+
+// Next's SWC transformer (the one next/jest wraps) and the mocks next/jest
+// used to inject, resolved from the PnP cache.
+const transformerPath = require.resolve('next/dist/build/swc/jest-transformer.js');
+const objectProxy = require.resolve('next/dist/build/jest/object-proxy.js');
+const styleMock = require.resolve('next/dist/build/jest/__mocks__/styleMock.js');
+const fileMock = require.resolve('next/dist/build/jest/__mocks__/fileMock.js');
+const nextFontMock = require.resolve('next/dist/build/jest/__mocks__/nextFontMock.js');
+const emptyMock = require.resolve('next/dist/build/jest/__mocks__/empty.js');
 
 /** @type {import('jest').Config} */
 const customJestConfig = {
@@ -16,24 +29,30 @@ const customJestConfig = {
   // Enable RTL matchers and router mocks
   setupFilesAfterEnv: ['<rootDir>/tests/jest.setup.js'],
   moduleNameMapper: {
-    // Support @/ alias → next/ path root
+    // CSS modules → proxy returning class names; plain css/style/fonts → mocks
+    '^.+\\.module\\.(css|sass|scss)$': objectProxy,
+    '^.+\\.(css|sass|scss)$': styleMock,
+    '^.+\\.(png|jpg|jpeg|gif|webp|avif|ico|bmp|svg)$': fileMock,
+    '@next/font/(.*)': nextFontMock,
+    'next/font/(.*)': nextFontMock,
+    '^server-only$': emptyMock,
+    // Support @/ alias → repo root
     '^@/(.*)$': '<rootDir>/$1',
   },
+  // Next's own SWC transformer (the one next/jest wraps), applied to source
+  // AND PnP-cached dependencies (see header note).
+  transform: {
+    '^.+\\.(js|jsx|ts|tsx|mjs)$': [transformerPath, {}],
+  },
+  transformIgnorePatterns: [
+    '^.+\\.module\\.(css|sass|scss)$',
+  ],
   testPathIgnorePatterns: [
     '<rootDir>/.next/',
-    '<rootDir>/node_modules/',
     '<rootDir>/tests/e2e/',
   ],
-  // Allow JSX in tests without explicit React import if using React 17+ JSX transform.
-  // Under Yarn PnP there are no real node_modules dirs — dependencies live in
-  // cache zips whose paths *contain* /node_modules/ segments, so excluding that
-  // pattern would skip transforming the ESM-only unified chain. Only the css
-  // module mocks (handled by next/jest) stay out of the transform.
-  transformIgnorePatterns: [
-    '^.+\\.module\\.(css|sass|scss)$',
-  ],
   // Make sure Jest can find our mocks
   moduleDirectories: ['node_modules', '<rootDir>'],
 };
 
-module.exports = createJestConfig(customJestConfig);
+module.exports = customJestConfig;