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

tools/testing/dart/test_suite.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Classes and methods for enumerating and preparing tests.
  *
  * This library includes:
  *
  * - Creating tests by listing all the Dart files in certain directories,
@@ skipping 228 matching lines @@
     globalTemporaryDirectory = globalTempDir;
 
     var filesRead = 0;
     void statusFileRead() {
       filesRead++;
       if (filesRead == statusFilePaths.length) {
         // Checked if we have already found and generated the tests for
         // 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
           // timer to make it so.
           void enqueueCachedTests(Timer ignore) {
             for (var info in testCache[suiteName]) {
               enqueueTestCaseFromTestInformation(info);
             }
             doDone();
           }
@@ skipping 124 matching lines @@
              Set<String> multitestOutcome = null]) {
       // Cache the test information for each test case.
       var info = new TestInformation(filename,
                                      optionsFromFile,
                                      isNegative,
                                      isNegativeIfChecked,
                                      hasFatalTypeErrors,
                                      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);
+      }
     };
   }
 
   void processFile(String filename) {
     if (!isTestFile(filename)) return;
 
     // Only run the tests that match the pattern.
     RegExp pattern = configuration['selectors'][suiteName];
     if (!pattern.hasMatch(filename)) return;
     if (filename.endsWith('test_config.dart')) return;
@@ skipping 456 matching lines @@
              "otherScripts": otherScripts,
              "isMultitest": isMultitest,
              "containsLeadingHash": containsLeadingHash,
              "isolateStubs": isolateStubs,
              "containsDomImport": containsDomImport,
              "isLibraryDefinition": isLibraryDefinition,
              "containsSourceOrImport": containsSourceOrImport,
              "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;
+  }  
 }
 
 
 class DartcCompilationTestSuite extends StandardTestSuite {
   List<String> _testDirs;
   int activityCount = 0;
 
   DartcCompilationTestSuite(Map configuration,
                             String suiteName,
                             String directoryPath,
@@ skipping 351 matching lines @@
  * $noCrash tests are expected to be flaky but not crash
  * $pass tests are expected to pass
  * $failOk tests are expected to fail that we won't fix
  * $fail tests are expected to fail that we should fix
  * $crash tests are expected to crash that we should fix
  * $timeout tests are allowed to timeout
 """;
     print(report);
    }
 }