Add createCallback to AsyncTestCase

Author: trowski

src/AsyncTestCase.php

@@ -3,6 +3,7 @@
 namespace Amp\PHPUnit;
 
 use Amp\Loop;
+use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase as PHPUnitTestCase;
 use function Amp\call;
 
@@ -78,4 +79,23 @@ final protected function setTimeout(int $timeout)
 
         Loop::unreference($this->timeoutId);
     }
+
+    /**
+     * @param int           $invocationCount Number of times the callback must be invoked or the test will fail.
+     * @param callable|null $returnCallback  Callable providing a return value for the callback.
+     *
+     * @return callable|MockObject Mock object having only an __invoke method.
+     */
+    final protected function createCallback(int $invocationCount, callable $returnCallback = null): callable
+    {
+        $mock = $this->createMock(CallbackStub::class);
+        $invocationMocker = $mock->expects($this->exactly($invocationCount))
+            ->method('__invoke');
+
+        if ($returnCallback) {
+            $invocationMocker->willReturnCallback($returnCallback);
+        }
+
+        return $mock;
+    }
 }

test/AsyncTestCaseTest.php

@@ -89,4 +89,13 @@ public function testSetMinimumRunTime()
         $this->expectExceptionMessageRegExp("/Expected test to take at least 100ms but instead took (\d+)ms/");
         yield call($func);
     }
+
+    public function testCreateCallback()
+    {
+        $mock = $this->createCallback(1, function (int $value): int {
+            return $value + 1;
+        });
+
+        $this->assertSame(2, $mock(1));
+    }
 }