Post summary: How to control what objects are being instantiated when using PowerMock.

This post is part of PowerMock series examples. The code shown in examples below is available in GitHub java-samples/junit repository.

Mock new object creation

You might have a method which instantiates some object and works with it. This case could be very tricky to automate because you do not have any control over this newly created object. This is where PowerMock comes to help to allow you to control what object is being created by replacing it with an object you can control.

Code to test

Below is a simple method where a new object is being created inside a method that has to be unit tested.

public class PowerMockDemo {

	public Point publicMethod() {
		return new Point(11, 11);
	}
}

Unit test

What we want to achieve in the unit test is to control instantiation of new Point object so that it is replaced with an object we have control over. The first thing to do is to annotate unit test with @RunWith(PowerMockRunner.class) telling JUnit to use PowerMock runner and with @PrepareForTest(PowerMockDemo.class) telling PowerMock to get inside PowerMockDemo class and prepare it for mocking. Mocking is done with PowerMockito.whenNew(Point.class).withAnyArguments().thenReturn(mockPoint). It tells PowerMock when a new object from class Point is instantiated with whatever arguments to return mockPoint instead. It is possible to return different objects based on different arguments Point is created with withArguments() method. Full code is below:

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.mockito.Mockito.mock;

@RunWith(PowerMockRunner.class)
@PrepareForTest(PowerMockDemo.class)
public class PowerMockDemoTest {

	private PowerMockDemo powerMockDemo;

	@Before
	public void setUp() {
		powerMockDemo = new PowerMockDemo();
	}

	@Test
	public void testMockNew() throws Exception {
		Point mockPoint = mock(Point.class);

		PowerMockito.whenNew(Point.class)
			.withAnyArguments().thenReturn(mockPoint);

		Point actualMockPoint = powerMockDemo.publicMethod();

		assertThat(actualMockPoint, is(mockPoint));
	}
}

Conclusion

PowerMock allows you to control want new objects are being created and replacing them with an object you have control over.

Related Posts

• PowerMock examples and why better not to use them

Post summary: How to mock private method with PowerMock by using spy object.

This post is part of PowerMock series examples. The code shown in examples below is available in GitHub java-samples/junit repository.

Mock private method

In some cases, you may need to alter the behavior of private method inside the class you are unit testing. You will need to mock this private method and make it return what needed for the particular case. Since this private method is inside your class under test then mocking it is little more specific. You have to use spy object.

Spy object

A spy is a real object which mocking framework has access to. Spied objects are partially mocked objects. Some their methods are real some mocked. I would say use spy object with great caution because you do not really know what is happening underneath and whether are you actually testing your class or mocked version of it.

Code to be tested

Below is a simple code that has a private method which created new Point object based on given as argument one. This private method is used to demonstrate how private methods can be called in Call private method with PowerMock post. In the current example, there is also a public method which calls this private method with a Point object.

public class PowerMockDemo {

	public Point callPrivateMethod() {
		return privateMethod(new Point(1, 1));
	}

	private Point privateMethod(Point point) {
		return new Point(point.getX() + 1, point.getY() + 1);
	}
}

Unit test

What we want to achieve in the unit test is to mock private method so that each call to it returns an object we have control over. The first thing to do is to annotate unit test with @RunWith(PowerMockRunner.class) telling JUnit to use PowerMock runner and with @PrepareForTest(PowerMockDemo.class) telling PowerMock to get inside PowerMockDemo class and prepare it for mocking. Then a spy object has to be created with PowerMockito.spy(new PowerMockDemo()). Actually, this is real PowerMockDemo object, but PowerMock is spying on it. The mocking of the private method is done with following code: PowerMockito.doReturn(mockPoint).when(powerMockDemoSpy, “privateMethod”, anyObject()). When “privateMethod” is called with whatever object then return mockPoint which is actually a mocked object. The full code example is shown below:

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.mockito.Matchers.anyObject;
import static org.mockito.Mockito.mock;

@RunWith(PowerMockRunner.class)
@PrepareForTest(PowerMockDemo.class)
public class PowerMockDemoTest {

	private PowerMockDemo powerMockDemoSpy;

	@Before
	public void setUp() {
		powerMockDemoSpy = PowerMockito.spy(new PowerMockDemo());
	}

	@Test
	public void testMockPrivateMethod() throws Exception {
		Point mockPoint = mock(Point.class);

		PowerMockito.doReturn(mockPoint)
			.when(powerMockDemoSpy, "privateMethod", anyObject());

		Point actualMockPoint = powerMockDemoSpy.callPrivateMethod();

		assertThat(actualMockPoint, is(mockPoint));
	}
}

Conclusion

PowerMock provides a way to mock private methods by using spy objects. Mockito also has spy objects, but they are not so powerful as PowerMock’s. One example is that PowerMock can spy on final objects.

Related Posts

• PowerMock examples and why better not to use them

Post summary: How to invoke a private method with PowerMock.

This post is part of PowerMock series examples. The code shown in examples below is available in GitHub java-samples/junit repository.

Unit test private method

Mainly public methods are being tested, so it is a very rare case where you want to unit test a private method. PowerMock provides utilities that can invoke private methods via a reflection and get output which can be tested.

Code to be tested

Below is a sample code that shows a class with a private method in it. It does nothing else but increases the X and Y coordinates of given as argument Point.

public class PowerMockDemo {

	private Point privateMethod(Point point) {
		return new Point(point.getX() + 1, point.getY() + 1);
	}
}

Unit test

Assume that this private method has to be unit tested for some reason. In order to do so, you have to use PowerMock’s Whitebox.invokeMethod(). You give an instance of the object, method name as a String and arguments to call the method with. In the example below argument is new Point(11, 11).

import org.junit.Before;
import org.junit.Test;
import org.powermock.reflect.Whitebox;

import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.MatcherAssert.assertThat;

public class PowerMockDemoTest {

	private PowerMockDemo powerMockDemo;

	@Before
	public void setUp() {
		powerMockDemo = new PowerMockDemo();
	}

	@Test
	public void testCallPrivateMethod() throws Exception {
		Point actual = Whitebox.invokeMethod(powerMockDemo, 
			"privateMethod", new Point(11, 11));

		assertThat(actual.getX(), is(12));
		assertThat(actual.getY(), is(12));
	}
}

Conclusion

PowerMock provides utilities which uses reflection to do certain things, as shown in the example above to invoke a private method.

Related Posts

• PowerMock examples and why better not to use them

Post summary: How to verify that static method was called during a unit test with PowerMock.

This post is part of PowerMock series examples. The code shown in examples below is available in GitHub java-samples/junit repository.

In Mock static methods in JUnit with PowerMock example post, I have given information about PowerMock and how to mock a static method. In the current post, I will demonstrate how to verify given static method was called during execution of a unit test.

Example class for unit test

We are going to unit test a class called LocatorService that internally uses a static method from utility class Utils. Method randomDistance(int distance) in Utils is returning random variable, hence it has no predictable behavior and the only way to test it is by mocking it:

public class LocatorService {

	public Point generatePointWithinDistance(Point point, int distance) {
		return new Point(point.getX() + Utils.randomDistance(distance), 
			point.getY() + Utils.randomDistance(distance));
	}
}

And Utils class is:

import java.util.Random;

public final class Utils {

	private static final Random RAND = new Random();

	private Utils() {
		// Utilities class
	}

	public static int randomDistance(int distance) {
		return RAND.nextInt(distance + distance) - distance;
	}
}

Nota bene: it is good code design practice to make utility classes final and with a private constructor.

Verify static method call

This is the full code. Additional details are shown below it.

package com.automationrhapsody.junit;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.internal.verification.VerificationModeFactory;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

@RunWith(PowerMockRunner.class)
@PrepareForTest(Utils.class)
public class LocatorServiceTest {

	private LocatorService locatorServiceUnderTest;

	@Before
	public void setUp() {
		PowerMockito.mockStatic(Utils.class);

		locatorServiceUnderTest = new LocatorService();
	}

	@Test
	public void testStaticMethodCall() {
		locatorServiceUnderTest
			.generatePointWithinDistance(new Point(11, 11), 1);
		locatorServiceUnderTest
			.generatePointWithinDistance(new Point(11, 11), 234);

		PowerMockito.verifyStatic(VerificationModeFactory.times(2));
		Utils.randomDistance(1);

		PowerMockito.verifyStatic(VerificationModeFactory.times(2));
		Utils.randomDistance(234);

		PowerMockito.verifyNoMoreInteractions(Utils.class);
	}
}

Explanation

Class containing static method should be prepared for mocking with PowerMockito.mockStatic(Utils.class) code. Then call to static method is done inside locatorServiceUnderTest .generatePointWithinDistance() method. In this test, it is intentionally called 2 times with different distance (1 and 234) in order to show the verification which consists of two parts. First part is PowerMockito.verifyStatic(VerificationModeFactory.times(2)) which tells PowerMock to verify static method was called 2 times. The second part is Utils.randomDistance(1) which tells exactly which static method should be verified. Instead of 1 in the brackets you can use anyInt() or anyObject(). 1 is used to make verification explicit. As you can see there is second verification that randomDistance() method was called with 234 as well: PowerMockito.verifyStatic(VerificationModeFactory.times(2)); Utils.randomDistance(234);.

Conclusion

PowerMock provides additional power to Mockito mocking library which is described in Mock JUnit tests with Mockito example post. In the current post, I have shown how to verify static method was called. It is very specific as verification actually consists of two steps.

Related Posts

• PowerMock examples and why better not to use them
• Mock static methods in JUnit with PowerMock example
• Mock JUnit tests with Mockito example