How to mock private static final instance variable using PowerMockRunner?

How to mock private static final instance variable using PowerMockRunner?

Let’s take a scenario which I worked upon recently,

Following is my actual JAVA source class,

WorkflowStream.java

public class WorkflowStream {

// How to Mock the below tightly coupled variable - DB service object??

private final static WorkflowDBClient workflowDBClient = WorkflowDBClient.getInstance();

public String createFlow(String data) {

boolean isUpdated = workflowDBClient.createRecord(data);

if (isUpdated) {

return "SUCCESS";

}

return "FAILED";

}

}


My simple Database class for demo purpose
WorkflowDBClient.java

public class WorkflowDBClient {

public static WorkflowDBClient getInstance() {

return new WorkflowDBClient();

}

public boolean createRecord(String data) {

return false;

}

}


Solution


import static org.junit.Assert.assertEquals;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.InjectMocks;
import org.mockito.Mockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
import org.powermock.reflect.Whitebox;

@RunWith(PowerMockRunner.class)
@PrepareForTest({ WorkflowStream.class })
public class WorkflowStreamTest {

@InjectMocks
WorkflowStream workflowStream;

WorkflowDBClient workflowDBClientMocked;

@Before
public void initMocks() throws Exception {

// Mocking the DB object

workflowDBClientMocked = Mockito.mock(WorkflowDBClient.class);

// Note: Original method returns FALSE. But below we Mocked to return TRUE

Mockito.when(workflowDBClientMocked.createRecord(Mockito.anyString())).thenReturn(true);

// Injecting the mocked DB service object into WorkflowStream

Whitebox.setInternalState(WorkflowStream.class, "workflowDBClient", workflowDBClientMocked);

}

@Test
public void createFlowTest() throws Exception {

String testData = "my input test record";

String status = workflowStream.createFlow(testData);

assertEquals(status, "SUCCESS");

}

}


Happy Learning 🙂