Monthly Archives: January 2014

Mock constructor

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Foreword

If you already read some other blog post about unusual mocking, you can skip prelude via this link.

I was asked to put together examples how to mock Java constructs well know for their testability issues:

I am calling these techniques unusual mocking. I was worried that such examples without any guidance can be widely used by teammates not deeply experienced in mocking frameworks.

Developers practicing TDD or BDD should be aware of testability problems behind these constructs and try to avoid them when designing their tests and modules. That is the reason why you probably wouldn’t be facing such unusual mocking often on project using these great programming methodologies.

But sometimes you have to extend or maintain legacy codebase that usually contains low cohesive classes. In most cases there isn’t time in current hectic agile world to make such class easy to unit test standard way. When you are trying to unit test such class you often realize that unusual mocking is needed.

That is why I decided to create and share refactoring considerations alongside with examples and workarounds for unusual mocking. Examples are using Mockito and PowerMock mocking frameworks and TestNG unit testing framework.

Mock constructor

Refactoring considerations

  • If your testing method creates instance/s of some type, there are two possibilities what can happen with these instances
    • Created instance/s are returned from testing method. They are in this case part of the testing method API. This can be tested by verifying against created instances rather than constructor method call. If target instances doesn’t have hashCode/equals contract implemented, you can still create test specific comparator to verify created data.
    • Created instances are used as parameter/s passed to some dependency object. This dependency object of testing class is most probably mocked. In this case it’s better idea to capture arguments of dependency method call and verify them. Mockito offers good support for this.
    • Created instances are temporary objects that support testing method job. In this case you shouldn’t care about creation of these instances, because you should treat testing module as black box that doing the job, but you don’t know how.
  • Create factory class for constructing instances and mock it standard way.
  • If that fits to requirement -> Abstract factory design pattern

Workaround using Mockito

This is my preferred technique when I need to mock constructor. I believe that minor exposing of internal implementation in flavor to enhance testability of testing module is much lower risk for project than fall into bytecode manipulation mocking  framework like PowerMock or JMockIt.

This technique involves:

  • Encapsulating the constructor into method with default access modifier
  • Partial mock (spy) is used to mock this method during testing

Mockito example covers:

  1. Partial mocking of factory method
  2. Verifying of mocked factory method call

Class under test:

public class CarFactoryMockito {
	Car carFactoryMethod(String type, String color) {
		return new Car(type, color);
	}

	public Car constructCar(String type, String color) {
		carFactoryMethod(type, color);
		// ... other logic needed to be tested ...
		return carFactoryMethod(type, color);
	}
}

Test:

public class CarFactoryMockitoTest {
	private static final String TESTING_TYPE = "Tatra";
	private static final String TESTING_COLOR = "Black";

	@Test
	public void testConstructCar() {
		CarFactoryMockito carFactory = new CarFactoryMockito();
		CarFactoryMockito carFactorySpy = Mockito.spy(carFactory);

		Car mockedInstance = Mockito.mock(Car.class);
		Mockito.doReturn(mockedInstance).when(carFactorySpy)
				.carFactoryMethod(TESTING_TYPE, TESTING_COLOR);

		// invoke testing method
		Car actualInstance = carFactorySpy.constructCar(TESTING_TYPE,
				TESTING_COLOR);

		Assert.assertEquals(actualInstance, mockedInstance);
		// ... verify other logic in constructCar() method ...
		Mockito.verify(carFactorySpy, Mockito.times(2)).carFactoryMethod(
				TESTING_TYPE, TESTING_COLOR);
	}
}

Usage of PowerMock

Before usage of this example, please carefully consider if it is worth to bring bytecode  manipulation risks into your project. They are gathered in this blog post. In my opinion it should be used only in very rare and non-avoidable cases.

Test shows how to mock constructor directly by PowerMock. Example covers:

  1. Mocking of constructor
  2. Verifying of constructor call

Class under test:

public class CarFactoryPowerMock {
	public Car constructCar(String type, String color) {
		new Car(type, color);
		return new Car(type, color);
	}
}

Test:

/**
 * Demonstrates constructor mocking by PowerMock.
 * <p>
 * NOTE: Prepared in PowerMock annotation {@link PrepareForTest} should be class
 * where is constructor called
 */
@PrepareForTest(CarFactoryPowerMock.class)
public class CarFactoryPowerMockTest extends PowerMockTestCase {
	private static final String TESTING_TYPE = "Tatra";
	private static final String TESTING_COLOR = "Black";

	@Test
	public void testConstructCar() throws Exception {
		Car expectedCar = Mockito.mock(Car.class);
		PowerMockito.whenNew(Car.class)
				.withArguments(TESTING_TYPE, TESTING_COLOR)
				.thenReturn(expectedCar);

		// invoke testing method
		CarFactoryPowerMock carFactory = new CarFactoryPowerMock();
		Car actualCar = carFactory.constructCar(TESTING_TYPE, TESTING_COLOR);

		Assert.assertEquals(actualCar, expectedCar);
		// ... verify other logic in constructCar() method ...
		PowerMockito.verifyNew(Car.class, Mockito.times(2)).withArguments(
				TESTING_TYPE, TESTING_COLOR);
	}
}

Links

Source code can be downloaded from Github.

Other unusual mocking examples:

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Mock private method

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Foreword

If you already read some other blog post about unusual mocking, you can skip prelude via this link.

I was asked to put together examples how to mock Java constructs well know for their testability issues:

I am calling these techniques unusual mocking. I was worried that such examples without any guidance can be widely used by teammates not deeply experienced in mocking frameworks.

Developers practicing TDD or BDD should be aware of testability problems behind these constructs and try to avoid them when designing their tests and modules. That is the reason why you probably wouldn’t be facing such unusual mocking often on project using these great programming methodologies.

But sometimes you have to extend or maintain legacy codebase that usually contains low cohesive classes. In most cases there isn’t time in current hectic agile world to make such class easy to unit test standard way. When you are trying to unit test such class you often realize that unusual mocking is needed.

That is why I decided to create and share refactoring considerations alongside with examples and workarounds for unusual mocking. Examples are using Mockito and PowerMock mocking frameworks and TestNG unit testing framework.

Mock private method

Refactoring considerations

Private method that is needed to be mocked can be in:

  • testing class (will call it TC)
  • direct dependency of testing class (will call is DDC)
  • class that is not direct dependency of testing module (will call it NDDC)

Re-factoring techniques to consider:

  • If the private method is in TC, it is a good sign that TC has low cohesion (has too many responsibilities) and logic behind private method should be extracted into separate class. After this refactoring, private method in TC becomes public in new dependency class. Than it is possible to mock it standard way.
  • If the private method is in DDC, concerns of TC and DDC modules are not separated properly. It means you are trying to test some logic from DDC in test for TC. Consider moving this logic to TC or to separate module. Private method than becomes public and can be mocked standard way.
  • If the private method is in NDDC, you are probably creating integration test instead of unit test. Unit test in theory should be testing module in isolation. That means to mock all direct dependencies (sometimes it’s easier to test with real objects when they are simple and independent enough). Consider:
    • Creation of unit test first. You can decide later if integration test is needed for group of modules you trying to test.
    • Find easier to mock boundaries for your integration test (you can find a clue in unit test for NDDC if exists)
    • Refactor NDDC according refactoring practises mentioned for TC and DDC above, update it’s unit test (also all tests affected by refactoring), and use created public method as boundary for your integration test.

Workaround using Mockito

This is my preferred technique when I need to mock private method. I believe that minor exposing of internal implementation in flavor to enhance testability of testing module is much lower risk for project than fall into bytecode manipulation mocking  framework like PowerMock or JMockIt.

This technique involves:

  • Changing private access modifier to default
  • Partially mock testing object by using spy

Mockito example covers:

  1. Mocking of changed default method with return value
  2. Mocking of changed changed default void method
  3. Verifying of changed default method calls

Class under test:

public class Train {
	public int compose() {
		for (int idx = 0; idx < getWagonsCount(); idx++) {
			addWagon(0);
		}
		return getWagonsCount();
	}

	/**
	 * Access modifier was changed from private to default to enhance
	 * testability
	 */
	// private
	int getWagonsCount() {
		throw new UnsupportedOperationException("Fail if not mocked!");
	}

	/**
	 * Access modifier was changed from private to default to enhance
	 * testability
	 */
	// private
	void addWagon(int position) {
		throw new UnsupportedOperationException(
				"Fail if not mocked! [position=" + position + "]");
	}
}

Test:

@Test
public void testCompose() {
	Train train = new Train();
	Train trainSpy = Mockito.spy(train);

	//notice different Mockito syntax for spy   
	Mockito.doReturn(TESTING_WAGON_COUNT).when(trainSpy).getWagonsCount();
	Mockito.doNothing().when(trainSpy).addWagon(0);

	// invoke testing method
	int actualWagonCount = trainSpy.compose();

	Assert.assertEquals(actualWagonCount, TESTING_WAGON_COUNT);
	Mockito.verify(trainSpy, Mockito.times(TESTING_WAGON_COUNT))
			.addWagon(0);
}

Usage of PowerMock

Before usage of this example, please carefully consider if it is worth to bring bytecode  manipulation risks into your project. They are gathered in this blog post. In my opinion it should be used only in very rare and non-avoidable cases.

Test shows how to mock private method directly by PowerMock. Example covers:

  1. Mocking of private method with return value
  2. Mocking of private void method
  3. Verifying of private method calls

Class under test:

public class Truck {
	public double addLoad(Collection<Double> boxWeightsToAdd) {
		for (Double boxWeight : boxWeightsToAdd) {
			addBoxToLoad(boxWeight);
		}
		return getLoadWeight();
	}

	private double getLoadWeight() {
		throw new UnsupportedOperationException("Fail is not mocked!");
	}

	private void addBoxToLoad(double weight) {
		throw new UnsupportedOperationException("Fail is not mocked! [weight="
				+ weight + "]");
	}
}

Test:

@PrepareForTest(Truck.class)
public class TruckTest extends PowerMockTestCase {
	private static final double TESTING_LOAD_WEIGHT = 200;
	private static final double TESTING_BOX_WEIGHT = 100;

	@Test
	public void testTestingMethod() throws Exception {
		Truck truck = new Truck();
		Truck truckSpy = PowerMockito.spy(truck);

		PowerMockito.doReturn(TESTING_LOAD_WEIGHT).when(truckSpy,
				"getLoadWeight");
		PowerMockito.doNothing().when(truckSpy, "addBoxToLoad",
				TESTING_BOX_WEIGHT);

		// call testing method
		Collection<Double> boxesWeights = Arrays.asList(TESTING_BOX_WEIGHT,
				TESTING_BOX_WEIGHT);
		double actualLoad = truckSpy.addLoad(boxesWeights);

		Assert.assertEquals(actualLoad, TESTING_LOAD_WEIGHT);
		PowerMockito.verifyPrivate(truckSpy, Mockito.times(2)).invoke(
				"addBoxToLoad", TESTING_BOX_WEIGHT);
	}
}

Links

Source code can be downloaded from Github.

Other unusual mocking examples:

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Enterprise Integration with Spring Certification study notes and hints

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Spring projects contain wide range of frameworks and abstraction APIs for Enterprise Integration. Best way to get an overview what Spring provides is to attend Enterprise Integration with Spring Training. It is unfortunately not affordable for everybody and I am not aware of any publication out there that explains Spring’s integration technologies altogether. Training includes:

  • Tasks and Scheduling support
  • Spring Remoting
  • Spring Web Services
  • Spring REST with Spring MVC
  • Spring JMS
  • Local and distributed transactions support
  • Spring Itegration
  • Spring Batch

I recently attended this course (thanks to my employer) and did certification exam afterwards. Now I would like to share my study notes and hints. These should provide you decent overview about Enterprise Integration with Spring. Study notes should cover everything needed for certification exam. But for passing the exam it isn’t enough just to memorize them. Unless you are familiar with these technologies already. They contain too many crucial information you can easily miss. You wouldn’t be successful until you get used each particular technology at least via examples or tutorials. I went through original SpringSource labs provided by training, few examples and tutorials. Also I was already familiar with Spring JMS, Spring MVC, Spring Integration and Spring transaction demarcation.

Study notes

  • Are based mainly on Spring reference documentations
  • Also contains some crucial principles and best practices Spring promotes that are usually not mentioned in reference documentations
  • Contains a lot of Spring XML configuration and Java code snippets
  • 57 pages
  • Download in PDF format
  • Download in ODT format (LibreOffice / OpenOffice)

Study hints, additional materials

Examples

Suggested readings

You can schedule certification exam via Pearson VUE site, find SpringSource and your local certification center. Exam ID is SpringEIwSCertV1.0.

Hope these materials help you also gain this badge:

Enterprise Integration with Spring

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