DZone
Performance Zone
Thanks for visiting DZone today,
Edit Profile
  • Manage Email Subscriptions
  • How to Post to DZone
  • Article Submission Guidelines
Sign Out View Profile
  • Post an Article
  • Manage My Drafts
Over 2 million developers have joined DZone.
Log In / Join
  • Refcardz
  • Trend Reports
  • Webinars
  • Zones
  • |
    • Agile
    • AI
    • Big Data
    • Cloud
    • Database
    • DevOps
    • Integration
    • IoT
    • Java
    • Microservices
    • Open Source
    • Performance
    • Security
    • Web Dev
DZone > Performance Zone > How to Unit Test Classes Which Create New Objects

How to Unit Test Classes Which Create New Objects

A simple method to write test cases for classes that use new keywords in their method with the help of Mockito and minimum code changes.

Shivam Mohan user avatar by
Shivam Mohan
CORE ·
Mar. 25, 20 · Performance Zone · Tutorial
Like (4)
Save
Tweet
76.19K Views

Join the DZone community and get the full member experience.

Join For Free

"Create"

Learn how to conduct effective unit tests.

First of all, I will start with a disclaimer that I am a strong proponent of using the simple factory programming idiom and by extension of using the Factory Method Pattern, instead of creating objects inside classes. The factory idiom helps you to insulate your code to changes thereby adhering to the Open to Extension Close to modification principle of object-oriented programming.

You may also like: Unit Testing: The Good, Bad, and Ugly

Also, the idea is to write testable code, not to write a hack to test code.

Having said that I will showcase a simple method to write test cases for classes that use new keywords in their method with the help of Mockito and minimum code changes.

Documentation link for Mockito.

The first step is to import Mockito dependencies into your code.

Java
 




x


 
1
<dependency>
2
   <groupId>org.mockito</groupId>
3
   <artifactId>mockito-core</artifactId>
4
   <version>2.23.0</version>
5
   <scope>test</scope>
6
</dependency>



Now let us see an example of how to test the class.

Let us assume the below is the class that we want to test.

Java
 




xxxxxxxxxx
1


 
1
public class ClassToBeTested {
2
    
3
    private ExternalClass object;
4
 
           
5
    public void MethodToTest() {
6
        object = new ExternalClass(arg1, arg2);
7
    }
8
}



Below is the sample class of the object that is instantiated in ClassToBeTested.

Java
 




xxxxxxxxxx
1


 
1
public class ExternalClass{
2
    private Object obj1;
3
    private Object obj2;
4
    public ExternalClass(Object arg1, Object arg2){
5
        this.obj1=arg1;
6
        this.obj2=arg2;
7
    }
8
}



The next step is to refactor the class to be tested and extract out the object instantiated into a separate method.

Java
 




xxxxxxxxxx
1
12


 
1
public class ClassToBeTested {
2
 
           
3
    private ExternalClass object;
4
 
           
5
    public ExternalClass makeExternalClassObject(Object arg1, Object arg2){
6
        return new ExternalClass(arg1, arg2);
7
    }
8
 
           
9
    public void MethodToTest() {
10
        object = makeExternalClassObject(arg1, arg2);
11
    }
12
}



One point to remember here is to avoid any logic in the make method so that we don’t have to write a unit test for this method.

Now let us write the test case for testing MethodToTest.

Java
 




xxxxxxxxxx
1
14


 
1
@RunWith(MockitoJUnitRunner.class)
2
public class ClassToBeTestedTest {
3
    @Mock private ExternalClass externalClass;
4
 
           
5
    @Test
6
    public void testMethodToBeTested(){
7
        ClassToBeTested classToBeTestedSpy = Mockito.spy(new ClassToBeTested());
8
        Mockito.doReturn(externalClass).when(classToBeTestedSpy)
9
                .makeExternalClassObject(arg1,arg2);
10
        classToBeTestedSpy.MethodToTest();
11
        /*Assertion Statement */
12
 
           
13
    }
14
}



Done! With this trick, we can write unit tests even for classes that have object instantiations in their implementation. Given that implementing the factory pattern is not feasible or not worth the effort.

Thanks!

Follow me on twitter at @IamShivamMohan

Further Reading

How to Automate a Java Unit Test, Including Mocking and Assertions

Creating Test Stages With JUnit

An Introduction to JUnit

unit test Object (computer science)

Opinions expressed by DZone contributors are their own.

Popular on DZone

  • Testing Schema Registry: Spring Boot and Apache Kafka With JSON Schema
  • What Is HttpSession in Servlets?
  • Instancio: Random Test Data Generator for Java (Part 1)
  • A Developer Evangelist's Thoughts on Angular 2

Comments

Performance Partner Resources

X

ABOUT US

  • About DZone
  • Send feedback
  • Careers
  • Sitemap

ADVERTISE

  • Advertise with DZone

CONTRIBUTE ON DZONE

  • Article Submission Guidelines
  • MVB Program
  • Become a Contributor
  • Visit the Writers' Zone

LEGAL

  • Terms of Service
  • Privacy Policy

CONTACT US

  • 600 Park Offices Drive
  • Suite 300
  • Durham, NC 27709
  • support@dzone.com
  • +1 (919) 678-0300

Let's be friends:

DZone.com is powered by 

AnswerHub logo