Add corelib tests

test/codegen/corelib/string_substring_test.dart

Index: test/codegen/corelib/string_substring_test.dart
diff --git a/test/codegen/corelib/string_substring_test.dart b/test/codegen/corelib/string_substring_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..7fd9091034d379b6bddffaef1f60732c7af7f00d
--- /dev/null
+++ b/test/codegen/corelib/string_substring_test.dart
@@ -0,0 +1,39 @@
+// Copyright (c) 2011, 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 "package:expect/expect.dart";
+
+main() {
+  // Test that not providing an optional argument goes to the end.
+  Expect.equals("".substring(0), "");
+  Expect.throws(() => "".substring(1),
+      (e) => e is RangeError);
+  Expect.throws(() => "".substring(-1),
+      (e) => e is RangeError);
+
+  Expect.equals("abc".substring(0), "abc");
+  Expect.equals("abc".substring(1), "bc");
+  Expect.equals("abc".substring(2), "c");
+  Expect.equals("abc".substring(3), "");
+  Expect.throws(() => "abc".substring(4),
+      (e) => e is RangeError);
+  Expect.throws(() => "abc".substring(-1),
+      (e) => e is RangeError);
+
+  // Test that providing null goes to the end.
+  Expect.equals("".substring(0, null), "");
+  Expect.throws(() => "".substring(1, null),
+      (e) => e is RangeError);
+  Expect.throws(() => "".substring(-1, null),
+      (e) => e is RangeError);
+
+  Expect.equals("abc".substring(0, null), "abc");
+  Expect.equals("abc".substring(1, null), "bc");
+  Expect.equals("abc".substring(2, null), "c");
+  Expect.equals("abc".substring(3, null), "");
+  Expect.throws(() => "abc".substring(4, null),
+      (e) => e is RangeError);
+  Expect.throws(() => "abc".substring(-1, null),
+      (e) => e is RangeError);
+}