Add workerd test for running unit tests under workerd

[kentonv]

Tests are written by defining an entrypoint with a method test(), similar to fetch():

export let mathTest = {
  async test(controller, env, ctx) {
    if (1 + 1 != 2) {
      throw new Error("math is broken");
    }
  }
}

Next, define a normal workerd configuration with this file as a service.

Then, do:

workerd test conf.capnp

All exported test() handlers will run. The test passes if none of them throw an exception.

Check out the sample included in this PR for a bit more detail.

Additionally, this PR adds a wd_test Bazel rule and even uses it to bring in one of our (previously-internal) API tests (blob-test).

TODO (in future PRs):

• The test log output is serviceable but very ugly at present.
• It's annoying for each test to be composed of two files, a capnp file and a js file. Can we either:
  • Auto-generate the capnp file? But what if special bindings are needed?
  • Create a new syntax that allows both to be specified in one file? Perhaps we should extend the capnp language to support a convenient form of large embedded text blobs? (The backtick-prefixed form is still a bit awkward for embedding whole files.)
• There is no support for tests in service workers syntax. Does this matter? Probably not.
• We need a convenient way to mock out fetch(). Should this be built-in, or a library? Probably a library, where you configure the global fetch() to loop back to a separate test entrypoint that implements the mock?
• How exactly should running tests under the inspector work? Do we need to pause and wait for the inspector to connect, or something?

[mikea]

do you think we can generate this file in most cases? Would be great to create just 1 file for test rather than two.

[kentonv]

I thought a lot about this. Many tests will need to customize the configuration, e.g. to test bindings, set up actors, or customize compat flags. I don't think we can avoid having some sort of way to specify configuration.

But I agree it would be nice to have the code and config in a single file. This is one of my future TODO points in the PR description.

One idea I've had is to introduce a new block-quote syntax in Cap'n Proto that is convenient for quoting large blocks of text, so that you could the JavaScript conveniently in the capnp file, like:

using Workerd = import "/workerd/workerd.capnp";

const unitTests :Workerd.Config = (
  services = [
    ( name = "blob-test",
      worker = (
        modules = [
          (name = "worker", esModule = .code)
        ],
        compatibilityDate = "2023-01-15",
      )
    ),
  ],
);

const code :Text = """
// JavaScript code here!
export default {
  async test(ctrl, env, ctx) {
    // ...
  }
}
"""

However, this might have some challenges when it comes to things like syntax highlighting?

Thoughts?

[dom96]

You could solve the syntax highlighting challenges by allowing something like this in capnp:

const code :Text = js"""
// JavaScript code here!
export default {
  async test(ctrl, env, ctx) {
    // ...
  }
}
"""

i.e. lang prefixes for string literals.

Though I personally don't think having two separate files is a big deal.

[mikea]

why not simply use <regex>?

[kentonv]

Globs are much easier to read and write than regexes, and I don't think this use case really needs the power of regexes.

[kentonv]

Ugh why does GitHub collapse force-pushes so stupidly?

Here's the changes I made since everyone reviewed:

https://github.com/cloudflare/workerd/compare/075ad9be198e638a10aa24a41ba1b0dc5599dddb..80aa2a2446679504b8d123e58a25b9c5545fc1d1

I also rebased on main.

[jasnell]

Still LGTM

[kentonv]

(rebased on main)