01-async-test-case.php

<?php

abstract class AsyncTestCase extends \PHPUnit\Framework\TestCase {
    public function runTest() {
        Loop::run(function() {
            $watcherId = Loop::delay(1500, function() {
                Loop::stop();
                $this->fail('The asynchronous test was expected to finish before the 1500 millisecond time limit');
            });

            $testReturn = parent::runTest();
            if (!$testReturn instanceof Promise) {
                $testReturn = new Success($testReturn);
            }
            yield $testReturn;
            Loop::cancel($watcherId);
        });
   }
}

02-test-context-test.php

<?php

class SomeAsyncTest extends AsyncTestCase {
    public function testTriggeringMultipleEventListeners() {
        $testContext = new TestContext();
        $testContext->requireCheckpoints(3);
        
        $subject = new EventBus();
        $subject->subscribe('foo', function($eventData) use($testContext) {
            // assert something about the state of the event data
            $testContext->checkpoint();
        });
        $subject->subscribe('foo', function($eventData) use($testContext) {
            // assert something about the state of the event data
            $testContext->checkpoint();
        });
        $subject->subscribe('foo', function($eventData) use($testContext) {
            // assert something about the state of the event data
            $testContext->checkpoint(); // Promise returned below would resolve here or fail in 1500ms
        });
        
        $subject->publish('foo', ['event', 'data']);
     
        // the $testContext acts like a Deferred and we can use it as such
        return $testContext->promise();
    }
}