document tests

Author: sw-yx

Diff for: README.md

@@ -48,7 +48,7 @@ It also watches your files and restarts the dev server on change. Note: if you a
 **IMPORTANT**:
 
 - You need a [`netlify.toml`](https://www.netlify.com/docs/netlify-toml-reference/) file with a `functions` field.
-- Every function needs to be a top-level js/ts/mjs file. You can have subfolders inside the `netlify-lambda` folder, but those are only for supporting files to be imported by your top level function.
+- Every function needs to be a top-level js/ts/mjs file. You can have subfolders inside the `netlify-lambda` folder, but those are only for supporting files to be imported by your top level function. Files that end with `.spec.*` or `.test.*` will be ignored so you can [colocate your tests](https://github.com/netlify/netlify-lambda/issues/99).
 - Function signatures follow the [AWS event handler](https://docs.aws.amazon.com/lambda/latest/dg/nodejs-prog-model-handler.html) syntax but must be named `handler`. [We use Node v8](https://www.netlify.com/blog/2018/04/03/node.js-8.10-now-available-in-netlify-functions/) so `async` functions **are** supported ([beware common mistakes](https://serverless.com/blog/common-node8-mistakes-in-lambda/)!). Read [Netlify Functions docs](https://www.netlify.com/docs/functions/#javascript-lambda-functions) for more info.
 
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