Implement --test_filter support

[cwybro]

Description

Implement --test_filter support, as detailed in #997. This can be engaged via a swift_test target like so:

bazel test //:Tests --test_filter=TestModuleName.TestClassName/testMethodName

Note: If --test_filter is not passed into the test invocation, we fallback to the original behavior (pass All into the xctest invocation.

Changelog

• IMPROVED:
  • Implement test_filter, allowing users to inject a specific test scope into swift_test execution

TODO

• Add tests
• Add docs (I'm open to updating / moving the new documentation as necessary)

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[cwybro]

@keith The current test suite validates the following:

1. Tests fail without test filtering
2. Test scope is reduced via test filtering

However 2 can currently be subverted if zero tests are executed (e.g. you specify a filter that matches no tests). Given this, I'd like to validate that the tests are actually executed, for example:

• The test.log contains: Test Suite 'All tests' / Test Suite 'Selected tests'
• The test.log contains: Executed 1 test, with 0 failures

Is it possible to write tests against the test log output (or another test artifact)? There might be a better way to assert against this output, or perhaps this is not a desirable test. Open to suggestions / feedback either way. Thanks!

[keith]

blah yea, i think you might be able to with a shell test, but that is worse in other ways, so i think this is probably good enough for now

[keith]

Thanks!