test_runner: mock_loader resolve the cjs and esm formats respectively.

lib/test/mock_loader.js

@@ -23,6 +23,8 @@ let debug = require('internal/util/debuglog').debuglog('test_runner', (fn) => {
   debug = fn;
 });
 const { createRequire, isBuiltin } = require('module');
+const { defaultGetFormatWithoutErrors } = require('internal/modules/esm/get_format');
+const { defaultResolve } = require('internal/modules/esm/resolve');
 
 // TODO(cjihrig): This file should not be exposed publicly, but register() does
 // not handle internal loaders. Before marking this API as stable, one of the
@@ -95,11 +97,20 @@ async function resolve(specifier, context, nextResolve) {
   if (isBuiltin(specifier)) {
     mockSpecifier = ensureNodeScheme(specifier);
   } else {
-    // TODO(cjihrig): This try...catch should be replaced by defaultResolve(),
-    // but there are some edge cases that caused the tests to fail on Windows.
+    let format;
+
+    if (context.parentURL) {
+      format = defaultGetFormatWithoutErrors(pathToFileURL(context.parentURL));
+    }
+
     try {
-      const req = createRequire(context.parentURL);
-      specifier = pathToFileURL(req.resolve(specifier)).href;
+      if (format === 'module') {
+        specifier = defaultResolve(specifier, context).url;
+      } else {
+        specifier = pathToFileURL(
+          createRequire(context.parentURL).resolve(specifier),
+        ).href;
+      }
     } catch {
       const parentURL = normalizeReferrerURL(context.parentURL);
       const parsedURL = URL.parse(specifier, parentURL)?.href;

test/fixtures/module-mocking/basic-esm-without-extension.js

@@ -0,0 +1 @@
+export let string = 'original esm string';

test/fixtures/module-mocking/wrong-import-after-module-mocking.js

@@ -0,0 +1,8 @@
+import { mock } from 'node:test';
+
+try {
+  mock.module?.('Whatever, this is not significant', { namedExports: {} });
+} catch {}
+
+const { string } = await import('./basic-esm-without-extension');
+console.log(`Found string: ${string}`); // prints 'original esm string'

test/parallel/test-runner-module-mocking.js

@@ -638,3 +638,18 @@ test('defaultExports work with ESM mocks in both module systems', async (t) => {
   assert.strictEqual((await import(fixture)).default, defaultExport);
   assert.strictEqual(require(fixture), defaultExport);
 });
+
+test('wrong import syntax should throw error after module mocking.', async () => {
+  const { stdout, stderr, code } = await common.spawnPromisified(
+    process.execPath,
+    [
+      '--experimental-test-module-mocks',
+      '--experimental-default-type=module',
+      fixtures.path('module-mocking/wrong-import-after-module-mocking.js'),
+    ]
+  );
+
+  assert.strictEqual(stdout, '');
+  assert.match(stderr, /Error \[ERR_MODULE_NOT_FOUND\]: Cannot find module/);
+  assert.strictEqual(code, 1);
+});