Add basic server smoke test

[alexrudd2]

Requires #170 since transient superagent silently dropped Node 12. (DefinitelyTyped/DefinitelyTyped#58445)

This is a basic smoke test to make sure the Express server starts (sometimes dependency updates break it). It currently works, but has a warning:

A worker process has failed to exit gracefully and has been force exited.
This is likely caused by tests leaking due to improper teardown. Try running with --detectOpenHandles to find leaks. Active timers can also cause this, ensure that .unref() was called on them.

I'm nearly certain this is caused by server.ts trying to connect to the EBB, but haven't quite figured out how to mock it out. Help would be appreciated.

[nornagon]

I assume this doesn't work because the server.ts code has an internal reference to ebbs, which doesn't get replaced by this mock. I'd recommend refactoring startServer to be more test-friendly by adding an optional argument which is a function to call to get the list of attached EBBs, defaulting to the internal ebbs function when not specified.

[alexrudd2]

More or less - the solution I came up with was exporting a function and then having the module import itself, which allows jest to mock that exported function. (In this case waitForEbb)

After various iterations, I think 3388136 mocks the least amount of code / runs the most "real" code. What do you think?

[alexrudd2]

> [email protected] test
> jest

 PASS  src/__tests__/planning.test.ts
 PASS  src/__tests__/util.test.ts
 PASS  src/__tests__/ebb.test.ts
 PASS  src/__tests__/server-smoke.test.ts
  ● Console

    console.log
      Server listening on http://[::]:61226

      at Server.<anonymous> (src/server.ts:233:15)

    console.log
      Found EBB at fake-ebb-path

      at ebbs_1 (src/server.ts:273:15)
          at ebbs_1.next (<anonymous>)


Test Suites: 4 passed, 4 total
Tests:       1 skipped, 13 passed, 14 total
Snapshots:   0 total
Time:        1.752 s, estimated 2 s
Ran all test suites.

[alexrudd2]

Closing in favor of #187