1. override
Future<Null> runTest(Future<Null> testBody(), VoidCallback invariantTester)

Call the testBody inside a FakeAsync scope on which pump can advance time.

Returns a future which completes when the test has run.

Called by the testWidgets and benchmarkWidgets functions to run a test.

The invariantTester argument is called after the testBody's Future completes. If it throws, then the test is marked as failed.

Source 

@override
Future<Null> runTest(Future<Null> testBody(), VoidCallback invariantTester) async {
  assert(!inTest);
  _inTest = true;
  return _runTest(testBody, invariantTester);
}