* 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.

Move tools tests into a general.shard directory in preparation to changing how we shard tools tests (#36108)

Rendering errors with root causes in the widget layer should have a reference to the widget (#32511)

Make FlutterError objects more structured so they can be displayed better in debugging tools such as Dart DevTools.

This changes the compiler output for gradle to be less verbose and more easily read.

This only applies to compilation error messages: other gradle messages will continue to print as before.

It also fixes a small problem with the performance measurement printing (see that "7.1s" on it's own line in the original?) so that if something is expected to have multiple lines of output, it prints an initial line, and a "Done" line with the elapsed time, so that it's possible to know what the time applies to.

It also updates the spinner to be fancier, at least on platforms other than Windows (which is missing a lot of symbols in its console font).

Addresses #17307

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* 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

* Ignore extraneous error messages outside of one skipped test

* Fix analysis error

...instead of the engine.

* enable lint prefer_asserts_in_initializer_lists

* enable --assert-initializer

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

This adds a way to run only a subset of the tests.
(The new flags do the same thing as 'pub run test'.)

`all.dart` is no longer needed. Furthermore, it causes tests to
be skipped, or to silently fail to run anything.

Fixes #7941

* Bump to test `0.12.20`.

Some test `0.12.20` highlights:
  * introduces `expectLater()`  that returns a `Future` that completes when the matcher has finished running
  * deprecates the `verbose` parameter to `expect()` and the `formatFailure()` (to be removed in `0.13.0`)

Otherwise:
  * to keep up w/ the deprecation of `verbose`, removes `widget_tester` API to pass `verbose` flag (alternatively we could suppress the warning for now)

* Update stack manipulation.

* Fix framecount.

...and fix bugs that the tests uncovered.

WRITE TEST FIND BUG

It was causing the flakiness because it was too short. The default timeout is better.

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 ensures that accidental usages of dart:io's
file API don't creep in over time.

This removes direct file access from within flutter_tools
in favor of using `package:file` via a `FileSystem` that's
accessed via the `ApplicationContext`.

This lays the groundwork for us to be able to easily swap
out the underlying file system when running Flutter tools,
which will be used to provide a record/replay file system,
analogous to what we have for process invocations.