Check in codegen test expectations.

test/codegen/expect/lib/html/transition_event_test.js

+dart_library.library('lib/html/transition_event_test', null, /* Imports */[
+  'dart_sdk',
+  'unittest'
+], function load__transition_event_test(exports, dart_sdk, unittest) {
+  'use strict';
+  const core = dart_sdk.core;
+  const html = dart_sdk.html;
+  const async = dart_sdk.async;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const html_individual_config = unittest.html_individual_config;
+  const unittest$ = unittest.unittest;
+  const src__matcher__expect = unittest.src__matcher__expect;
+  const src__matcher__core_matchers = unittest.src__matcher__core_matchers;
+  const transition_event_test = Object.create(null);
+  let TransitionEventTodynamic = () => (TransitionEventTodynamic = dart.constFn(dart.functionType(dart.dynamic, [html.TransitionEvent])))();
+  let VoidTovoid = () => (VoidTovoid = dart.constFn(dart.functionType(dart.void, [])))();
+  let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
+  let VoidTovoid$ = () => (VoidTovoid$ = dart.constFn(dart.definiteFunctionType(dart.void, [])))();
+  let dynamicTodynamic = () => (dynamicTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [dart.dynamic])))();
+  let const$;
+  transition_event_test.main = function() {
+    html_individual_config.useHtmlIndividualConfiguration();
+    unittest$.group('supported', dart.fn(() => {
+      unittest$.test('supported', dart.fn(() => {
+        src__matcher__expect.expect(html.CssStyleDeclaration[dartx.supportsTransitions], true);
+      }, VoidTodynamic()));
+    }, VoidTovoid$()));
+    unittest$.group('functional', dart.fn(() => {
+      unittest$.test('transitionEnd', dart.fn(() => {
+        if (dart.test(html.CssStyleDeclaration[dartx.supportsTransitions])) {
+          let element = html.DivElement.new();
+          html.document[dartx.body][dartx.append](element);
+          element[dartx.style][dartx.opacity] = '0';
+          element[dartx.style][dartx.width] = '100px';
+          element[dartx.style][dartx.height] = '100px';
+          element[dartx.style][dartx.background] = 'red';
+          element[dartx.style][dartx.transition] = 'opacity .1s';
+          async.Timer.new(const$ || (const$ = dart.const(new core.Duration({milliseconds: 100}))), VoidTovoid()._check(unittest$.expectAsync(dart.fn(() => {
+            element[dartx.onTransitionEnd].first.then(dart.dynamic)(TransitionEventTodynamic()._check(unittest$.expectAsync(dart.fn(e => {
+              src__matcher__expect.expect(html.TransitionEvent.is(e), src__matcher__core_matchers.isTrue);
+              src__matcher__expect.expect(dart.dload(e, 'propertyName'), 'opacity');
+            }, dynamicTodynamic()))));
+            element[dartx.style][dartx.opacity] = '1';
+          }, VoidTodynamic()))));
+        }
+      }, VoidTodynamic()));
+    }, VoidTovoid$()));
+  };
+  dart.fn(transition_event_test.main, VoidTodynamic());
+  // Exports:
+  exports.transition_event_test = transition_event_test;
+});