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

node_modules/undici/docs/best-practices/writing-tests.md

@@ -0,0 +1,20 @@
+# Writing tests
+
+Undici is tuned for a production use case and its default will keep
+a socket open for a few seconds after an HTTP request is completed to
+remove the overhead of opening up a new socket. These settings that makes
+Undici shine in production are not a good fit for using Undici in automated
+tests, as it will result in longer execution times.
+
+The following are good defaults that will keep the socket open for only 10ms:
+
+```js
+import { request, setGlobalDispatcher, Agent } from 'undici'
+
+const agent = new Agent({
+  keepAliveTimeout: 10, // milliseconds
+  keepAliveMaxTimeout: 10 // milliseconds
+})
+
+setGlobalDispatcher(agent)
+```