Mockito provides an Answer interface that allows stubbing with a generic interface.
Syntax
//add the behavior to add numbers
when(calcService.add(20.0,10.0)).thenAnswer(new Answer<Double>() {
@Override
public Double answer(InvocationOnMock invocation) throws Throwable {
//get the arguments passed to mock
Object[] args = invocation.getArguments();
//get the mock
Object mock = invocation.getMock();
//return the result
return 30.0;
}
});
Example
Step 1 − Create an interface called CalculatorService to provide mathematical functions
File: CalculatorService.java
public interface CalculatorService {
public double add(double input1, double input2);
public double subtract(double input1, double input2);
public double multiply(double input1, double input2);
public double divide(double input1, double input2);
}
Step 2 − Create a JAVA class to represent MathApplication
File: MathApplication.java
public class MathApplication {
private CalculatorService calcService;
public void setCalculatorService(CalculatorService calcService){
this.calcService = calcService;
}
public double add(double input1, double input2){
return calcService.add(input1, input2);
}
public double subtract(double input1, double input2){
return calcService.subtract(input1, input2);
}
public double multiply(double input1, double input2){
return calcService.multiply(input1, input2);
}
public double divide(double input1, double input2){
return calcService.divide(input1, input2);
}
}
Step 3 − Test the MathApplication class
Let’s test the MathApplication class, by injecting in it a mock of calculatorService. Mock will be created by Mockito.
Here we’ve added one mock method call, add() to the mock object via when(). However, during testing, we’ve called subtract() before calling add(). When we create a mock object using Mockito.createStrictMock(), the order of execution of the method does matter.
File: MathApplicationTester.java
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;
import static org.mockito.Mockito.inOrder;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.InOrder;
import org.mockito.runners.MockitoJUnitRunner;
// @RunWith attaches a runner with the test class to initialize the test data
@RunWith(MockitoJUnitRunner.class)
public class MathApplicationTester {
private MathApplication mathApplication;
private CalculatorService calcService;
@Before
public void setUp(){
mathApplication = new MathApplication();
calcService = mock(CalculatorService.class);
mathApplication.setCalculatorService(calcService);
}
@Test
public void testAdd(){
//add the behavior to add numbers
when(calcService.add(20.0,10.0)).thenAnswer(new Answer<Double>() {
@Override
public Double answer(InvocationOnMock invocation) throws Throwable {
//get the arguments passed to mock
Object[] args = invocation.getArguments();
//get the mock
Object mock = invocation.getMock();
//return the result
return 30.0;
}
});
//test the add functionality
Assert.assertEquals(mathApplication.add(20.0, 10.0),30.0,0);
}
}
Step 4 − Execute test cases
Create a java class file named TestRunner in C:\> Mockito_WORKSPACE to execute Test case(s).
File: TestRunner.java
import org.junit.runner.JUnitCore;
import org.junit.runner.Result;
import org.junit.runner.notification.Failure;
public class TestRunner {
public static void main(String[] args) {
Result result = JUnitCore.runClasses(MathApplicationTester.class);
for (Failure failure : result.getFailures()) {
System.out.println(failure.toString());
}
System.out.println(result.wasSuccessful());
}
}
Step 5 − Verify the Result
Compile the classes using the javac compiler as follows −
C:\Mockito_WORKSPACE>javac CalculatorService.java MathApplication.
java MathApplicationTester.java TestRunner.java
Now run the Test Runner to see the result −
C:\Mockito_WORKSPACE>java TestRunner
Verify the output.
true
