Add support for sharding test runs.

test/runner/shard_test.dart

Index: test/runner/shard_test.dart
diff --git a/test/runner/shard_test.dart b/test/runner/shard_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..541687c0447827cd058c0da3667bcbc86a408b61
--- /dev/null
+++ b/test/runner/shard_test.dart
@@ -0,0 +1,169 @@
+// Copyright (c) 2016, 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.
+
+@TestOn("vm")
+
+import 'package:scheduled_test/descriptor.dart' as d;
+import 'package:scheduled_test/scheduled_stream.dart';
+import 'package:scheduled_test/scheduled_test.dart';
+
+import 'package:test/src/util/exit_codes.dart' as exit_codes;
+
+import '../io.dart';
+
+void main() {
+  useSandbox();
+
+  test("divides all the tests among the available shards", () {
+    d.file("test.dart", """
+      import 'package:test/test.dart';
+
+      void main() {
+        test("test 1", () {});
+        test("test 2", () {});
+        test("test 3", () {});
+        test("test 4", () {});
+        test("test 5", () {});
+        test("test 6", () {});
+        test("test 7", () {});
+        test("test 8", () {});
+        test("test 9", () {});
+        test("test 10", () {});
+      }
+    """).create();
+
+    var test = runTest(["test.dart", "--shard-index=0", "--total-shards=3"]);
+    test.stdout.expect(containsInOrder([
+      "+0: test 1",
+      "+1: test 2",
+      "+2: test 3",
+      "+3: All tests passed!"
+    ]));
+    test.shouldExit(0);
+
+    test = runTest(["test.dart", "--shard-index=1", "--total-shards=3"]);
+    test.stdout.expect(containsInOrder([
+      "+0: test 4",
+      "+1: test 5",
+      "+2: test 6",
+      "+3: test 7",
+      "+4: All tests passed!"
+    ]));
+    test.shouldExit(0);
+
+    test = runTest(["test.dart", "--shard-index=2", "--total-shards=3"]);
+    test.stdout.expect(containsInOrder([
+      "+0: test 8",
+      "+1: test 9",
+      "+2: test 10",
+      "+3: All tests passed!"
+    ]));
+    test.shouldExit(0);
+  });
+
+  test("shards each suite", () {
+    d.file("1_test.dart", """
+      import 'package:test/test.dart';
+
+      void main() {
+        test("test 1.1", () {});
+        test("test 1.2", () {});
+        test("test 1.3", () {});
+      }
+    """).create();
+
+    d.file("2_test.dart", """
+      import 'package:test/test.dart';
+
+      void main() {
+        test("test 2.1", () {});
+        test("test 2.2", () {});
+        test("test 2.3", () {});
+      }
+    """).create();
+
+    var test = runTest([".", "--shard-index=0", "--total-shards=3"]);
+    test.stdout.expect(inOrder([
+      either(containsInOrder([
+        "+0: ./1_test.dart: test 1.1",
+        "+1: ./2_test.dart: test 2.1"
+      ]), containsInOrder([
+        "+0: ./2_test.dart: test 2.1",
+        "+1: ./1_test.dart: test 1.1"
+      ])),
+      contains("+2: All tests passed!")
+    ]));
+    test.shouldExit(0);
+
+
+    test = runTest([".", "--shard-index=1", "--total-shards=3"]);
+    test.stdout.expect(inOrder([
+      either(containsInOrder([
+        "+0: ./1_test.dart: test 1.2",
+        "+1: ./2_test.dart: test 2.2"
+      ]), containsInOrder([
+        "+0: ./2_test.dart: test 2.2",
+        "+1: ./1_test.dart: test 1.2"
+      ])),
+      contains("+2: All tests passed!")
+    ]));
+    test.shouldExit(0);
+
+    test = runTest([".", "--shard-index=2", "--total-shards=3"]);
+    test.stdout.expect(inOrder([
+      either(containsInOrder([
+        "+0: ./1_test.dart: test 1.3",
+        "+1: ./2_test.dart: test 2.3"
+      ]), containsInOrder([
+        "+0: ./2_test.dart: test 2.3",
+        "+1: ./1_test.dart: test 1.3"
+      ])),
+      contains("+2: All tests passed!")
+    ]));
+    test.shouldExit(0);
+  });
+
+  test("an empty shard reports success", () {
+    d.file("test.dart", """
+      import 'package:test/test.dart';
+
+      void main() {
+        test("test 1", () {});
+        test("test 2", () {});
+      }
+    """).create();
+
+    var test = runTest(["test.dart", "--shard-index=1", "--total-shards=3"]);
+    test.stdout.expect(consumeThrough("No tests ran."));
+    test.shouldExit(0);
+  });
+
+  group("reports an error if", () {
+    test("--shard-index is provided alone", () {
+      var test = runTest(["--shard-index=1"]);
+      test.stderr.expect(
+          "--shard-index and --total-shards may only be passed together.");
+      test.shouldExit(exit_codes.usage);
+    });
+
+    test("--total-shards is provided alone", () {
+      var test = runTest(["--total-shards=5"]);
+      test.stderr.expect(
+          "--shard-index and --total-shards may only be passed together.");
+      test.shouldExit(exit_codes.usage);
+    });
+
+    test("--shard-index is negative", () {
+      var test = runTest(["--shard-index=-1", "--total-shards=5"]);
+      test.stderr.expect("--shard-index may not be negative.");
+      test.shouldExit(exit_codes.usage);
+    });
+
+    test("--shard-index is equal to --total-shards", () {
+      var test = runTest(["--shard-index=5", "--total-shards=5"]);
+      test.stderr.expect("--shard-index must be less than --total-shards.");
+      test.shouldExit(exit_codes.usage);
+    });
+  });
+}