CP-2241 Audit test suite for performance and coverage

[evanweible-wf]

The test suite has grown the point where CI builds take >5 mins. It's time to revisit the test suite and optimize wherever possible.

• Get as much coverage as possible with unit tests. Our unit tests leverage the mock configurations and as a result, each test takes only a few milliseconds.

• Remove as much overlap in coverage as possible between unit tests and integration tests. In other words, get rid of integration tests that only cover code already covered by unit tests.

• Leverage tags and whole-package configuration to increase timeouts/delays only for tests that absolutely need it.

  Use Case: currently, the WebSocket integration tests have one or more 200ms delays in many of the tests because because the SockJS integration server seems to require the extra time. However, the native WebSocket integration server seems to propagate events faster and wouldn't require such a large delay.

• Optimize the integration servers. In particular, the SockJS server is suspiciously slow. There may be a memory leak at play that is causing this sluggish performance.

• Reach 100% coverage. In the past there were a couple of lines that couldn't be covered, but I think with the latest Dart SDK and updated coverage package, it should be possible.

  Previously, we couldn't cover a few lines in the browser configuration of the MultipartRequest class because the File class could not be constructed manually.

  Additionally, older versions of the coverage package seemed to report one or two lines as uncovered when they should have been covered or were not even applicable lines of code.