* Add a test for a directory instead of a single test.

* Add test data to a child directory to test the command.

* Add test data to a child directory to test the command.

* Add test data to a child directory to test the command.

* Correct test.

This reverts commit 71e9bd6f.

* Upgrade everything except matcher.
* Roll matcher (and test)
* Adjust tests that depend on flutter:test directly to depend on a shim
* Require use of package:test shim and remove other references to package:test

Also, add tests to verify that our coverage is actually being tested!

We now produce a more reasonable error message when we're missing the
flutter_test dependency in a test. Also, remove the flutter_tools stack traces
when the engine dies.

Fixes #6187

This patch adds a new test harness and a first, trivial test to run with the
harness. The new test harness is built on package:test and should run on
Travis. Over time, we'll migrate our existing tests into this harness.