PowerMockito mock indirect static method

Question

Class to test

public class Randomer {
    public int get() {
        return (int) Math.random() + 1;
    }
}

The test class

package org.samiron;

import static org.junit.Assert.assertEquals;

import org.junit.runner.RunWith;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.api.support.membermodification.MemberMatcher;
import org.powermock.api.support.membermodification.MemberModifier;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
import org.testng.annotations.Test;

/**
 * @author samiron
 *
 */
@RunWith(PowerMockRunner.class)
@PrepareForTest({ Randomer.class, Math.class })
public class RandomerTest {

    @Test
    public void shouldAddUpDieRollsCorrectly() throws Exception {
        PowerMockito.spy(Math.class);
        MemberModifier.stub(MemberMatcher.method(Math.class, "random")).toReturn(2.0);
        Randomer d = new Randomer();
        assertEquals(3, d.get());
    }
}

Always getting java.lang.AssertionError: expected:<3> but was:<1>

Whats going wrong here? To be honest, every time I came across a situation to mock a static function I try to find a way around instead of wasting time. So need your help to figure out the exact solution.

The sole purpose of the example classes is to demonstrate that Math.random() function is not mocked and therefore not returning the desired value.

General realization

Mocking is a every essential tool while writing tests. Although mocking on instances works quite as expected but mocking static methods seems to be a real complicated with so many combinations of mocking libraries and so many options to support just few simple scenarios. This should be streamlined.

Libraries used:

• mockito-all-1.9.5.jar
• powermock-mockito-release-full-1.5.1-full.jar

Answer 1

There seems to be a library mismatch here.

In the comments you stated to use the following dependencies (without the convenience of Maven):

<dependency>
  <groupId>org.mockito</groupId>
  <artifactId>mockito-all</artifactId>
  <version>1.9.5</version>
  <scope>test</scope>
</dependency>

<dependency>
  <groupId>org.powermock</groupId>
  <artifactId>powermock-mockito-release-full</artifactId>
  <version>1.5.1</version>
  <scope>test</scope>
</dependency>

I got your code working using these:

<dependency>
  <groupId>org.powermock</groupId>
  <artifactId>powermock-module-junit4</artifactId>
  <version>1.7.0</version>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.powermock</groupId>
  <artifactId>powermock-api-mockito</artifactId>
  <version>1.7.0</version>
  <scope>test</scope>
</dependency>

Answer 2

This test passes thereby proving that the static call Math.random() is successfully mocked:

@RunWith(PowerMockRunner.class)
// tell PowerMock about (a) the class you are going to test and (b) the class you are going to 'mock static'
@PrepareForTest({Randomer.class, Math.class })
public class RandomerTest {

    @Test
    public void shouldAddUpDieRollsCorrectly() throws Exception {
        // prepare PowerMock for mocking statics on Math
        PowerMockito.mockStatic(Math.class);
        // establish an expectation for what Match.random() should return
        PowerMockito.when(Math.random()).thenReturn(2.0);

        Randomer d = new Randomer();

        assertEquals(3, d.get());
    }
}

The main differences between this and what you posted in your question are is that I am using ...

• PowerMockito.mockStatic(Math.class) and PowerMockito.when(Math.random()).thenReturn(2.0)

... instead of:

• PowerMockito.spy(Math.class) and MemberModifier.stub(MemberMatcher.method(Math.class, "random")).toReturn(2.0)

Also, in your OP the example code uses a mixture of JUnit (org.powermock.modules.junit4.PowerMockRunner) and TestNG (org.testng.annotations.Test) whereas in my example I am just using JUnit.

The above has been verified with

• junit:4.12
• powermock-module-junit4:1.7.0
• powermock-api-mockito2:1.7.0