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/something.js

@@ -0,0 +1,10 @@
+// Unless explicitly stated otherwise all files in this repository are licensed under the Apache 2.0 License.
+//
+// This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2021 Datadog, Inc.
+
+'use strict'
+
+module.exports = function bar () {
+  return 42
+}
+module.exports.foo = 42