Mockito is an open source testing framework which allows to create mock objects.
Mockito can be used to create mock for an interface or a class.
A mock can be thought as a dummy implementation of an interface or a class which is used to define/change its behavior.
Examples
pom.xml<dependency>
<groupId>org.mockito</groupId>
<artifactId>mockito-core</artifactId>
<version>3.3.3</version>
</dependency>
An example interface
package com.logicbig.example;
public interface MyService {
public int doSomething();
}
Mocking the interface in a test
package com.logicbig.example;
import org.junit.Assert;
import org.junit.Test;
import org.mockito.Mockito;
public class MyServiceTest {
@Test
public void testDoSomething(){
MyService mock = Mockito.mock(MyService.class);
int i = mock.doSomething();
Assert.assertEquals(i, 0);
}
}
D:\mockito-getting-started-creating-mocks>mvn test -Dtest="MyServiceTest"
[INFO] Scanning for projects...
[INFO]
[INFO] ----< com.logicbig.example:mockito-getting-started-creating-mocks >-----
[INFO] Building mockito-getting-started-creating-mocks 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ mockito-getting-started-creating-mocks ---
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO]
[INFO] --- maven-compiler-plugin:3.8.1:compile (default-compile) @ mockito-getting-started-creating-mocks ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ mockito-getting-started-creating-mocks ---
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO]
[INFO] --- maven-compiler-plugin:3.8.1:testCompile (default-testCompile) @ mockito-getting-started-creating-mocks ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ mockito-getting-started-creating-mocks ---
-------------------------------------------------------
T E S T S
-------------------------------------------------------
Running com.logicbig.example.MyServiceTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.913 sec
Results :
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4.188 s
[INFO] Finished at: 2020-04-17T00:11:00-05:00
[INFO] ------------------------------------------------------------------------
By default a mock's method returns either null, a primitive/primitive wrapper value, or an empty collection.
For example 0 for an int/Integer and false for a boolean/Boolean.
Stubbing methods
Subbing is defining of what values to return when we invoke methods of a mock object.
Stubbing is achieved by Mockito's when-thenReturn methods.
Let's see how to do stubbing for our interface MyInterface:
package com.logicbig.example;
import org.junit.Assert;
import org.junit.Test;
import org.mockito.Mockito;
public class MyServiceTest2 {
@Test
public void testDoSomething2(){
MyService mock = Mockito.mock(MyService.class);
Mockito.when(mock.doSomething()).thenReturn(10);//stubbing
int i = mock.doSomething();
Assert.assertEquals(i, 10);
}
}
D:\mockito-getting-started-creating-mocks>mvn test -Dtest="MyServiceTest2"
[INFO] Scanning for projects...
[INFO]
[INFO] ----< com.logicbig.example:mockito-getting-started-creating-mocks >-----
[INFO] Building mockito-getting-started-creating-mocks 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ mockito-getting-started-creating-mocks ---
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO]
[INFO] --- maven-compiler-plugin:3.8.1:compile (default-compile) @ mockito-getting-started-creating-mocks ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ mockito-getting-started-creating-mocks ---
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO]
[INFO] --- maven-compiler-plugin:3.8.1:testCompile (default-testCompile) @ mockito-getting-started-creating-mocks ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ mockito-getting-started-creating-mocks ---
-------------------------------------------------------
T E S T S
-------------------------------------------------------
Running com.logicbig.example.MyServiceTest2
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.916 sec
Results :
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4.132 s
[INFO] Finished at: 2020-04-17T00:10:42-05:00
[INFO] ------------------------------------------------------------------------
A more meaningful example
Following is another application class which uses MyService instance:
package com.logicbig.example;
public class MyProcessor {
private MyService myService;
public MyProcessor(MyService myService) {
this.myService = myService;
}
public String process() {
int returnInteger = myService.doSomething();
return String.format("My Integer is: " + returnInteger);
}
}
Let's mock MyService again to test MyProcessor#process() method:
package com.logicbig.example;
import org.junit.Assert;
import org.junit.Test;
import org.mockito.Mockito;
public class ProcessorTest {
@Test
public void processTest() {
MyService myService = Mockito.mock(MyService.class);
Mockito.when(myService.doSomething()).thenReturn(10);
MyProcessor myProcessor = new MyProcessor(myService);
String returnedValue = myProcessor.process();
Assert.assertEquals(returnedValue, "My Integer is: 10");
}
}
D:\mockito-getting-started-creating-mocks>mvn test -Dtest="ProcessorTest"
[INFO] Scanning for projects...
[INFO]
[INFO] ----< com.logicbig.example:mockito-getting-started-creating-mocks >-----
[INFO] Building mockito-getting-started-creating-mocks 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ mockito-getting-started-creating-mocks ---
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO]
[INFO] --- maven-compiler-plugin:3.8.1:compile (default-compile) @ mockito-getting-started-creating-mocks ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ mockito-getting-started-creating-mocks ---
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO]
[INFO] --- maven-compiler-plugin:3.8.1:testCompile (default-testCompile) @ mockito-getting-started-creating-mocks ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ mockito-getting-started-creating-mocks ---
-------------------------------------------------------
T E S T S
-------------------------------------------------------
Running com.logicbig.example.ProcessorTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.694 sec
Results :
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.798 s
[INFO] Finished at: 2020-04-17T00:20:03-05:00
[INFO] ------------------------------------------------------------------------
Example ProjectDependencies and Technologies Used: - mockito-core 3.3.3: Mockito mock objects library core API and implementation.
- junit 4.13: JUnit is a unit testing framework for Java, created by Erich Gamma and Kent Beck.
- JDK 8
- Maven 3.5.4
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