Report more heuristics for tests that require manual work.

tools/migration/lib/src/validate.dart

+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'log.dart';
+
+final _unittestPattern = "package:unittest";
+final _checkedPattern = new RegExp(r"\bchecked\b");
+final _abstractErrorPattern =
+    new RegExp(r"\bAbstractClassInstantiationError\b");
+final _typeErrorPattern = new RegExp(r"\bTypeError\b");
+
+void validateFile(String path, String source, [List<String> todos]) {
+  check(Pattern pattern, String noteMessage, String todo) {
+    if (!source.contains(pattern)) return;
+    note("${bold(path)} $noteMessage.");
+    if (todos != null) todos.add(todo);
+  }
+
+  check(_unittestPattern, "uses the unittest package", "Migrate off unittest.");
+  check(_checkedPattern, 'mentions "checked"',
+      'Fix code that mentions "checked" mode.');
+  check(_abstractErrorPattern, 'mentions "AbstractClassInstantiationError"',
+      "Remove code that checks for AbstractClassInstantiationError.");
+  check(_typeErrorPattern, 'mentions "TypeError"',
+      "Remove code that checks for TypeError.");
+}