Update test framework: fix run_tests.py to support all test files, add auto-import-check for test files

node_modules/import-in-the-middle/test/fixtures/import.mjs

@@ -0,0 +1,23 @@
+import { register } from 'module'
+import { Hook, createAddHookMessageChannel } from '../../index.js'
+// We've imported path here to ensure that the hook is still applied later even
+// if the library is used here.
+import * as path from 'path'
+
+const { registerOptions, waitForAllMessagesAcknowledged } = createAddHookMessageChannel()
+
+register('../../hook.mjs', import.meta.url, registerOptions)
+
+Hook(['path'], (exports) => {
+  exports.sep = '@'
+})
+
+Hook(['os'], (exports) => {
+  exports.arch = function () {
+    return 'new_crazy_arch'
+  }
+})
+
+console.assert(path.sep !== '@')
+
+await waitForAllMessagesAcknowledged()