* 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.
Prep to get us ready to pull in a new dev SDK and bump our analyzer DEP.
* updates `crypto` (required by fresh analyzer)
* fixes newly flagged dead code warnings
* fixes switches that fall through and don't return
This makes it possible to substitute 'flutter run' for 'flutter test'
and actually watch a test run on a device.
For any test that depends on flutter_test:
1. Remove any import of 'package:test/test.dart'.
2. Replace `testWidgets('...', (WidgetTester tester) {`
with `testWidgets('...', (WidgetTester tester) async {`
3. Add an "await" in front of calls to any of the following:
* tap()
* tapAt()
* fling()
* flingFrom()
* scroll()
* scrollAt()
* pump()
* pumpWidget()
4. Replace any calls to `tester.flushMicrotasks()` with calls to
`await tester.idle()`.
There's a guarding API that you can use, if you have particularly
complicated tests, to get better error messages. Search for
TestAsyncUtils.
