Mocha adapter for Polymer browser tests.

chrome/test/data/webui/mocha_adapter.js

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @fileoverview A mocha adapter for BrowserTests. To use, include mocha.js and
+ * mocha_adapter.js in a WebUIBrowserTest's extraLibraries array.
+ */
+
+/**
+ * Initializes a mocha reporter for the BrowserTest framework, which registers
+ * event listeners on the given Runner.
+ * @constructor
+ * @param {Runner} runner Runs the tests and provides hooks for test results
+ *     (see Runner.prototype in mocha.js).
+ */
+function BrowserTestReporter(runner) {
+  var passes = 0;
+  var failures = 0;
+
+  // Increment passes for each passed test.
+  runner.on('pass', function(test) {
+    passes++;

[Dan Beam, 2015/06/02 18:11:16]

what if a test accidentally passes twice and another never passes?

[michaelpg, 2015/06/02 19:32:59]

All that junk is handled for free! Mocha throws an error if a test times out or
if a test calls done() multiple times.

+  });
+
+  // Report failures. Mocha only catches "assert" failures, because "expect"
+  // failures are caught by test_api.js.
+  runner.on('fail', function(test, err) {
+    failures++;
+    var message = 'Mocha test failed: ' + test.fullTitle() + '\n';
+
+    // We don't need tracing past the first line pointing to mocha.js.
+    var stack = err.stack.split('\n');
+    for (var i = 0; i < stack.length; i++) {
+      if (stack[i].indexOf('(mocha.js:') != -1)
+        break;
+    }
+    // Include the stack up to the first function from mocha.js.
+    if (i < stack.length)
+      message += stack.slice(0, i + 1).join('\n');
+    else
+      message += err.stack;
+
+    console.error(message);
+  });
+
+  // Report the results to the test API.
+  runner.on('end', function() {
+    if (failures == 0) {
+      testDone();
+      return;
+    }
+    testDone([
+      false,
+      'Test Errors: ' + failures + '/' + (passes + failures) +
+      ' tests had failed assertions.'
+    ]);
+  });
+}
+
+// Configure mocha.
+mocha.setup({
+  // Use TDD interface instead of BDD.
+  ui: 'tdd',
+  // Use custom reporter to interface with BrowserTests.
+  reporter: BrowserTestReporter,
+});