Add a way to mark a failed test case

[asashour]

Use case

Sometimes there is a need to commit a test case, before actually implementing it.

As part of Test-driven development, this has the benefit of:

• Agreeing first if a scenario is a correct with expected behavior, before starting the implementation.
• One may lack the implementation knowledge, but a test case could be easier to contribute.
• Having a single place of all reported issues (in one file), instead of searching in github issues.
• When an implementation is (accidentally) fixed, a failing test would point to the tracked issue to be closed.

Some other projects use the same concept (notYetImplemented), e.g. Groovy and Selenium.

Needles to say, this doesn't mean implementation is done without testing. But it means tests can be committed, and implementation can later follow.

A similar request in test in dart-lang/test#1178

Proposal

An optional FAILING to be added to the lints comment (optionally having an issue number), and when set, the result of the test is reversed.

• If the test fails (as expected) then the build will be green
• If the implementation succeeds, then the build is red complaining Test XYZ is marked as failing but already succeeds.

void false_negative() {
  noLintTriggered(); // LINT FAILING
}
void false_posivite() {
  incorrectLintTriggered(); // OK FAILING dart-lang/linter#1234
}

As a side note, it seems Annotation.message is not used by any lint, except in annotation_test, and so it could be removed.