Add language tests for Issue 18628.

As suggested by @karlklose in https://codereview.chromium.org/513563002/
comments.

Improve testing documentation.

- add a README
- add a description by example of selectors to the "./tools/test.py -h"
  output
- update/add source comments

I had a hard time figuring out how to add and run the tests, mostly
because I tried to call them "*_test_1.dart" and "*_test_2.dart", but
language test files must have names of the form "*_test.dart".  So, I
added a README summarizing and referencing the relevant docs.

R=brianwilkerson@google.com, karlklose@google.com, jwren@google.com
BUG=

Review URL: https://codereview.chromium.org//521773003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@39822 260f80e4-7a28-3924-810f-c04153c831b5

tests/README

@@ -0,0 +1,43 @@
+Run Existing Tests
+==================
+
+See the output of
+
+  ../tools/test.py --help
+
+for how to run tests.
+
+See also
+
+  https://code.google.com/p/dart/wiki/Building#Testing
+
+for detailed examples.
+
+Create New Tests
+================
+
+See comments above
+
+  factory StandardTestSuite.forDirectory
+
+in
+
+  ../tools/testing/dart/test_suite.dart
+
+for the default test directory layout. By default test-file names must
+end in "_test.dart", but some test suites, such as ./co19, subclass
+StandardTestSuite and override this default.
+
+See comments at the beginning of
+
+  ../tools/testing/dart/multitest.dart
+
+for how to create tests that pass by failing with a known error. For
+example,
+
+  ...
+  int x = "not an int"; /// 01: static type warning
+  ...
+
+as part of a test will only pass the "--compiler dartanalyzer" test if
+the assignment generates a static type warning.

tests/language/issue18628_1_test.dart

@@ -0,0 +1,20 @@
+// 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.
+
+// This test checks for a regression found in Dart Editor: the
+// analyzer was treating [Type] as more specific than any type
+// variable (generic parameter).
+//
+// https://code.google.com/p/dart/issues/detail?id=18628
+
+class C<T> {
+  // This line is supposed to cause the warning; the other commented
+  // line just doesn't make sense without this line.
+  T t = int; /// 01: static type warning
+}
+
+main() {
+  C<Type> c = new C<Type>();
+  print(c.t); /// 01: static type warning
+}

tests/language/issue18628_2_test.dart

@@ -0,0 +1,20 @@
+// 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.
+
+// This test checks for a regression found in Dart Editor: the
+// analyzer was treating [Type] as more specific than any type
+// variable (generic parameter).
+//
+// https://code.google.com/p/dart/issues/detail?id=18628
+
+class X<T extends Type> {}
+
+// This line is supposed to cause the warning; the other lines are
+// marked because they don't make sense when [Y] is not defined.
+class Y<U> extends X<U> {} /// 01: static type warning
+
+main() {
+  X<Type> x = new X<Type>(); /// 01: static type warning
+  Y<Type> y = new Y<Type>(); /// 01: static type warning
+}

tools/test.dart

@@ -18,8 +18,12 @@
  * and passses along all command line arguments to this script.)
  *
  * The command line args of this script are documented in
- * "tools/testing/test_options.dart".
+ * "tools/testing/dart/test_options.dart"; they are printed
+ * when this script is run with "--help".
  *
+ * The default test directory layout is documented in
+ * "tools/testing/dart/test_suite.dart", above
+ * "factory StandardTestSuite.forDirectory".
  */
 
 library test;

tools/testing/dart/test_options.dart

@@ -823,7 +823,13 @@ Note: currently only implemented for dart2js.''',
    * Print out usage information.
    */
   void _printHelp() {
-    print('usage: dart test.dart [options]\n');
+    print('usage: dart test.dart [options] [selector]');
+    print('');
+    print('The optional selector limits the tests that will be run.');
+    print('For example, the selector "language/issue", or equivalently');
+    print('"language/*issue*", limits to test files matching the regexp');
+    print('".*issue.*\\.dart" in the "tests/language" directory.');
+    print('');
     print('Options:\n');
     for (var option in _options) {
       print('${option.name}: ${option.description}.');