How to test a method of a class with constructor arguments using Mockito/Powermock

Question

I have a Mockito/PowerMockito issue!

The class to test is as below:

public class ClassToTest {

    private String string;

    public ClassToTest(String s) {
        this.string = s;
    }

    public String concatenate() {
        return string.concat(" - Done!");
    }

    public ClassToTest create(String s) {
        return new ClassToTest(s);
    }
}

The test class i wrote:

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

@RunWith(PowerMockRunner.class)
@PrepareForTest(ClassToTest.class)
public class ClassToTestTest {

    @Test
    public void concatenate() throws Exception {
        ClassToTest classToTest = Mockito.mock(ClassToTest.class);
        PowerMockito.whenNew(ClassToTest.class).withArguments(Mockito.anyString()).thenReturn(classToTest);
        classToTest.concatenate();
    }
}

Question - How do i set a value of the instance variable named "string" from test class so that i can test concatenate method(concatenate method uses the constructor initialized "string" variable") Currently the debug point is not even going inside concatenate() method. I need to do this with either mockito/powermock.

Note - The example I have given is a representation of the issue i am facing in real time.

Any leads would help me.

Thanks in advance!!

Answer 1

Your test is pointless for several reasons.

1. you mock the class you're trying to test
2. you mock a method that is not even called in the test
3. you don't verify the result of the method you call.

Your test can just be

ClassToTest tested = new ClassToTest("test"); // create instance
String concatResult = tested.concatenate();   // call method under test
assertThat(concatResult).isEqualTo("test - Done");  // verify result

No need to mock anything. If you want to test the create method (of which I don't see the point at all btw), you can do

ClassToTest tested = new ClassToTest(""); // the String is never used anyway
ClassToTest created = tested.create("test"); // call method under test
assertThat(created.concatenate()).isEqualTo("test - Done"); // verify

If you mock classes you're testing, you don't test the classes behavior, but only the mocked result. Consider

Don't do this

ClassToTest mock = mock(ClassToTest.class);
ClassToTest other = mock(ClassToTest.class);
when(mock.create(anyString()).thenReturn(other);
when(other.concatenate(anyString()).thenReturn("expected");
ClassToTest created = mock.create("test");
String result = created.concatenate("lala");
assertThat(result).isEqualTo("expected"); // duh