Mockito provides a Answer interface which allows stubbing with generic interface.
Syntax
//add the behavior to add numbers
@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 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
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 a mock of calculatorService in it. Mock will be created by Mockito.
Here we've added one mock method calls, add() to the mock object via when().
File: MathApplicationTester.java
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.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 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