Require tests be both in /test/ and end _test.dart
Require tests be both in /test/ and end _test.dart

Fixes #2034.
Fixes #2021.
Also see #1165.

Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code