EasyMock - Overview

What is Mocking?

Mocking is a way to test the functionality of a class in isolation. Mocking does not require a database connection or properties file read or file server read to test a functionality. Mock objects do the mocking of the real service. A mock object returns a dummy data corresponding to some dummy input passed to it.

EasyMock - Environment Setup

EasyMock is a framework for Java, so the very first requirement is to have JDK installed in your machine.

EasyMock - First Application

Before going into the details of the EasyMock Framework, let’s see an application in action. In this example, we've created a mock of Stock Service to get the dummy price of some stocks and unit tested a java class named Portfolio.

EasyMock - JUnit Integration

In this chapter, we'll learn how to integrate JUnit and EasyMock together. Here we will create a Math Application which uses CalculatorService to perform basic mathematical operations such as addition, subtraction, multiply, and division.

EasyMock - Adding Behavior

EasyMock adds a functionality to a mock object using the methods expect() and expectLassCall(). Take a look at the following code snippet.

//add the behavior of calc service to add two numbers
EasyMock.expect(calcService.add(10.0,20.0)).andReturn(30.00);

EasyMock - Verifying Behavior

EasyMock can ensure whether a mock is being used or not. It is done using the verify() method. Take a look at the following code snippet.

//activate the mock
EasyMock.replay(calcService);

EasyMock - Expecting Calls

EasyMock provides a special check on the number of calls that can be made on a particular method. Suppose MathApplication should call the CalculatorService.serviceUsed() method only once, then it should not be able to call CalculatorService.serviceUsed() more than once.

EasyMock - Varying Calls

EasyMock provides the following additional methods to vary the expected call counts.

• times (int min, int max) – expects between min and max calls.
• atLeastOnce () – expects at least one call.
• anyTimes () – expects an unrestricted number of calls.
  

EasyMock - Exception Handling

EasyMock provides the capability to a mock to throw exceptions, so exception handling can be tested. Take a look at the following code snippet.

//add the behavior to throw exception

EasyMock - createMock

So far, we've used annotations to create mocks. EasyMock provides various methods to create mock objects. EasyMock.createMock() creates mocks without bothering about the order of method calls that the mock is going to make in due course of its action.

EasyMock - createStrictMock

EasyMock.createStrictMock() creates a mock and also takes care of the order of method calls that the mock is going to make in due course of its action.

Syntax

calcService = EasyMock.createStrictMock(CalculatorService.class);

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 EasyMock.
Here we've added two mock method calls, add() and subtract(), to the mock object via expect(). However during testing, we've called subtract() before calling add(). When we create a mock object using EasyMock.createStrictMock(), the order of execution of the method does matter.
File: MathApplicationTester.java

import org.easymock.EasyMock;
import org.easymock.EasyMockRunner;

import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;

@RunWith(EasyMockRunner.class)
public class MathApplicationTester {
 
   private MathApplication mathApplication;
   private CalculatorService calcService;
   
   @Before
   public void setUp(){
      mathApplication = new MathApplication();
      calcService = EasyMock.createStrictMock(CalculatorService.class);
      mathApplication.setCalculatorService(calcService);
   }

   @Test
   public void testAddAndSubtract(){
      
      //add the behavior to add numbers
      EasyMock.expect(calcService.add(20.0,10.0)).andReturn(30.0);
      
      //subtract the behavior to subtract numbers
      EasyMock.expect(calcService.subtract(20.0,10.0)).andReturn(10.0);
      
      //activate the mock
      EasyMock.replay(calcService); 
 
      //test the subtract functionality
      Assert.assertEquals(mathApplication.subtract(20.0, 10.0),10.0,0);
      
      //test the add functionality
      Assert.assertEquals(mathApplication.add(20.0, 10.0),30.0,0);
      
      //verify call to calcService is made or not
      EasyMock.verify(calcService);
   }
}

Step 4: Execute test cases
Create a java class file named TestRunner in C:\> EasyMock_WORKSPACE to execute Test case(s).
File: TestRunner.java

EasyMock - createNiceMock

EasyMock.createNiceMock() creates a mock and sets the default implementation of each method of the mock. If EasyMock.createMock() is used, then invoking the mock method throws assertion error.

EasyMock - EasyMockSupport

EasyMockSupport is a utility or helper class for test classes. It provides the following functionalities:

• replayAll() – Registers all the created mocks in one batch.
• verifyAll() – Verifies all the mock operations in one batch.
• resetAll() – Resets all the mock operations in one batch.

EasyMock - Quick Guide

EasyMock - Overview

What is Mocking?

Mocking is a way to test the functionality of a class in isolation. Mocking does not require a database connection or properties file read or file server read to test a functionality. Mock objects do the mocking of the real service. A mock object returns a dummy data corresponding to some dummy input passed to it.

EasyMock

EasyMock - Useful Resources

The following resources contain additional information on EasyMock. Please use them to get more in-depth knowledge on this topic.

Discuss EasyMock

EasyMock is a mocking framework, JAVA-based library that is used for effective unit testing of JAVA applications. EasyMock is used to mock interfaces so that a dummy functionality can be added to a mock interface that can be used in unit testing.