Please help me with Mock Objects.

[fatabass]

Please do not close this thread.

My code:

package com.tugay.learningjunit;

public class MyClass {
	
	RandomNumberGenerator randomNumberGenerator = new RandomNumberGenerator();
	
	public int shoot(){
		int someNumber = randomNumberGenerator.generateRandomNumber();
		return someNumber*2;
	}
}

package com.tugay.learningjunit;

import java.util.Random;

public class RandomNumberGenerator {
	public int generateRandomNumber(){
		return new Random().nextInt(15);
	}
}

I am trying to test the shoot() method. Since it generated a random integer every time, I am trying something like this:

package com.tugay.tests;

import junit.framework.Assert;

import org.junit.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import static org.mockito.Mockito.when;

import com.tugay.learningjunit.MyClass;
import com.tugay.learningjunit.RandomNumberGenerator;

public class MyClassTester {

	@InjectMocks
	private MyClass myObject = new MyClass();

	@Mock
	private RandomNumberGenerator randomNumberGenerator;

	@Test
	public void testShoot() {

		when(randomNumberGenerator.generateRandomNumber()).thenReturn(3);

		try {
			int resultingNumber = myObject.shoot();
			Assert.assertEquals(6, resultingNumber);
		} catch (Exception e) {

		}

}
}

But I am getting an error saying:
java.lang.NullPointerException
at com.tugay.tests.MyClassTester.testShoot(MyClassTes ter.java:24)

When I try with:

private RandomNumberGenerator randomNumberGenerator = new RandomNumberGenerator();

then I get:

org.mockito.exceptions.misusing.MissingMethodInvoc ationException:
when() requires an argument which has to be 'a method call on a mock'.
For example:
when(mock.getArticles()).thenReturn(articles);

Also, this error might show up because:
1. you stub either of: final/private/equals()/hashCode() methods.
Those methods *cannot* be stubbed/verified.
2. inside when() you don't call method on mock but on some other object.
3. the parent of the mocked class is not public.
It is a limitation of the mock engine.


How can I force to return generateRandomNumber() method to return 3?

Please help. Thank you.

[fatabass]

I added the line @RunWith(MockitoJUnitRunner.class) on top of public class MyClassTester and it works fine now.
Interesting.
Thanks anyway.