Testing exceptions

Introduction

Mockito provides the functionality of a mock that throws exceptions. This allows us to perform exception handling.
This blog will help you understand Exception handling in Mockito with an example.

Exception Handling-Example

Step 1 − Creating interface CalculatorMain that provide mathematical functions

File: CalculatorMain.java

public interface CalculatorMain {
   public double add(double inp1, double inp2);
   public double subtraction(double inp1, double inp2);
   public double multiplication (double inp1, double inp2);
   public double division(double inp1, double inp2);
}

Step 2 − Creating a class to represent MathApp

File: MathApp.java

public class MathApp {
   private CalculatorMain calcService;


   public void setCalculatorMain(CalculatorMain calcService){
      this.calcService = calcService;
   }
   
   public double add(double inp1, double inp2){
      return calcService.add(inp1, inp2); 
   }
   
   public double subtraction(double inp1, double inp2){
      return calcService.subtraction(inp1, inp2);
   }
   
   public double multiplication (double inp1, double inp2){
      return calcService.multiplication (inp1, inp2);
   }
   
   public double division(double inp1, double inp2){
      return calcService.division(inp1, inp2);
   }
}

Step 3 − Testing the MathApp class.

Let's test the MathApp class by injecting in it a mock of CalculatorMain. Mockito will create a mock.

File: MathAppTester.java

import static org.mockito.Mockito.doThrow;
import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.runners.MockitoJUnitRunner;

// @RunWith will attach a runner to the test class that will // initialize the test data
@RunWith(MockitoRunner.class)
public class MathAppTester {

   // @TestSubject in mockito is an annotation used to identify // a class 
     // that is going to use the mock object
   @TestSubject
   MathApp MathApp = new MathApp();

   //@Mock in Mockito is an annotation used to create a mock object that is to be injected
   @Mock
   CalculatorMain calcService;

   @Test(expected = RuntimeException.class)
   public void testAdd(){
      //This adds the behavior to throw exception
      doThrow(new RuntimeException("Add operation not implemented"))
         .when(calcService).add(10.0,20.0);

      //This tests the add functionality
      Assert.assertEquals(MathApp.add(10.0, 20.0),30.0,0); 
   }
}

Step 4 − Executing test cases.

Next, we create a java class file called TestRunner in C:\> Mockito_WORKSPACE to execute Test cases.

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(MathAppTester.class);
      
      for (Failure failure : result.getFailures()) {
         System.out.println(failure.toString());
      }
   
      System.out.println(result.wasSuccessful());
   }
} 

Step 5 − Verifying the Result

Finally, we compile the classes using the javac compiler.

C:\Mockito_WORKSPACE>javac CalculatorMain.java CalculatorMain.java MathAppTester.java TestRunner.java

Now run the Test Runner to see the result −

C:\Mockito_WORKSPACE>java TestRunner

Verify the output.

testAdd(MathAppTester): Add operation not implemented

false