Shard tests run by test.dart, so they can be distributed to multiple machines.

tools/testing/dart/test_suite.dart

Index: tools/testing/dart/test_suite.dart
diff --git a/tools/testing/dart/test_suite.dart b/tools/testing/dart/test_suite.dart
index 4bbd4f41e68941e3fa7c5691e16e3c0937fc745e..a911e9043844e09c05ad7eacb48d249ecfac80ba 100644
--- a/tools/testing/dart/test_suite.dart
+++ b/tools/testing/dart/test_suite.dart
@@ -246,6 +246,16 @@ class StandardTestSuite implements TestSuite {
         // this suite.
         if (!testCache.containsKey(suiteName)) {
           cachedTests = testCache[suiteName] = [];
+          if (configuration['shards'] > 1) {

[Mads Ager (google), 2012/03/23 23:38:20]

You should add a comment about how this works for sharding. No tests are
actually enqueued and when all tests have been listed the doDone function is
called because there are no tests enqueued to run. At that point, all tests are
know and we compute the shard and enqueue the tests for this shard. 

[Bill Hesse, 2012/03/28 22:46:19]

Done.

+            Function oldDone = doDone;
+            doDone = () {
+              testCache[suiteName] = shardTests();
+              for (var info in testCache[suiteName]) {
+                enqueueTestCaseFromTestInformation(info);
+              }
+              oldDone();
+            };
+          }            
           processDirectory();
         } else {
           // We rely on enqueueing completing asynchronously so use a
@@ -390,7 +400,10 @@ class StandardTestSuite implements TestSuite {
                                      hasRuntimeErrors,
                                      multitestOutcome);
       cachedTests.add(info);
-      enqueueTestCaseFromTestInformation(info);
+      if (configuration['shards'] == 1) {
+        // If we are not sharding, we queue the tests as we find them.
+        enqueueTestCaseFromTestInformation(info);
+      }
     };
   }
 
@@ -867,6 +880,23 @@ class StandardTestSuite implements TestSuite {
              "numStaticTypeAnnotations": numStaticTypeAnnotations,
              "numCompileTimeAnnotations": numCompileTimeAnnotations};
   }
+
+  /**
+   * shardTests takes the list of tests, stored as the List<TestInformation> cachedTests,
+   * and selects only the tests belonging to this shard.  The tests are sorted by filename,
+   * and if there are n shards and we are shard number i, only the tests at indices equal to

[Bill Hesse, 2012/03/23 22:33:56]

Fix long lines in this function.

[Bill Hesse, 2012/03/28 22:46:19]

Done.

+   * i-1 modulo n are kept.
+   */
+  List<TestInformation> shardTests() {
+    cachedTests.sort((TestInformation a, TestInformation b) => a.filename.compareTo(b.filename));
+    int n = configuration['shards'];
+    int i = configuration['shard'];
+    if (n >= 2) {
+      int current = 0;
+      cachedTests = cachedTests.filter((t) => ++current % n == i - 1);

[Mads Ager (google), 2012/03/23 23:38:20]

I would add some parenthesis here to help the reader.

[Bill Hesse, 2012/03/28 22:46:19]

Done.

+    }
+    return cachedTests;
+  }  
 }