Mocha adapter for Polymer browser tests.

chrome/test/data/webui/mocha_adapter.js

Index: chrome/test/data/webui/mocha_adapter.js
diff --git a/chrome/test/data/webui/mocha_adapter.js b/chrome/test/data/webui/mocha_adapter.js
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+// 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++;
+  });
+
+  // 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';
+
+    // Remove unhelpful mocha lines from stack trace.
+    var stack = err.stack.split('\n');
+    for (var i = 0; i < stack.length; i++) {
+      if (stack[i].indexOf('mocha.js:') == -1)
+        message += stack[i] + '\n';
+    }
+
+    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,
+});