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/env.mjs

@@ -0,0 +1,8 @@
+let env = { FOO: 'baz' }
+
+function setEnv (newEnv) {
+  console.log('setting env, env.FOO is', newEnv.FOO)
+  env = newEnv
+}
+
+export { setEnv, env }