unittest: refactor ahead of matcher changes

lib/src/throws_matchers.dart

+// Copyright (c) 2014, 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.
+
+library unittest.throws_matchers;
+
+import 'package:matcher/matcher.dart' hide Throws;
+
+import 'throws_matcher.dart';
+
+/// A matcher for functions that throw ArgumentError.
+const Matcher throwsArgumentError = const Throws(isArgumentError);
+
+/// A matcher for functions that throw ConcurrentModificationError.
+const Matcher throwsConcurrentModificationError =
+    const Throws(isConcurrentModificationError);
+
+/// A matcher for functions that throw CyclicInitializationError.
+const Matcher throwsCyclicInitializationError =
+    const Throws(isCyclicInitializationError);
+
+/// A matcher for functions that throw Exception.
+const Matcher throwsException = const Throws(isException);
+
+/// A matcher for functions that throw FormatException.
+const Matcher throwsFormatException = const Throws(isFormatException);
+
+/// A matcher for functions that throw NoSuchMethodError.
+const Matcher throwsNoSuchMethodError = const Throws(isNoSuchMethodError);
+
+/// A matcher for functions that throw NullThrownError.
+const Matcher throwsNullThrownError = const Throws(isNullThrownError);
+
+/// A matcher for functions that throw RangeError.
+const Matcher throwsRangeError = const Throws(isRangeError);
+
+/// A matcher for functions that throw StateError.
+const Matcher throwsStateError = const Throws(isStateError);
+
+/// A matcher for functions that throw Exception.
+const Matcher throwsUnimplementedError = const Throws(isUnimplementedError);
+
+/// A matcher for functions that throw UnsupportedError.
+const Matcher throwsUnsupportedError = const Throws(isUnsupportedError);