When can use Mockito's when-thenThrow or doThrow-when methods to stub exceptions.
Examples
Example application
package com.logicbig.example;
public interface MyService {
public int doSomething();
public int doSomething2() throws Exception;
}
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);
}
public String process2() throws Exception {
int returnInteger = myService.doSomething2();
return String.format("My Integer is: " + returnInteger);
}
public String process3() {
try {
int returnInteger = myService.doSomething2();
return String.format("My Integer is: " + returnInteger);
} catch (Exception e) {
System.out.println("-- exception thrown in MyProcess --");
return "default-value";
}
}
}
Testing exceptions
Testing unchecked exception
package com.logicbig.example;
import junit.framework.TestCase;
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()).thenThrow(new RuntimeException("Cannot process"));
MyProcessor myProcessor = new MyProcessor(myService);
try {
String returnedValue = myProcessor.process();
TestCase.fail();
}catch (Exception e){
System.out.println("-- exception thrown --");
Assert.assertTrue(e instanceof RuntimeException);
Assert.assertEquals(e.getMessage(), "Cannot process");
}
}
}
D:\mockito-throwing-exception-in-subbing>mvn test -Dtest="ProcessorTest"
[INFO] Scanning for projects...
[INFO]
[INFO] -----< com.logicbig.example:mockito-throwing-exception-in-subbing >-----
[INFO] Building mockito-throwing-exception-in-subbing 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ mockito-throwing-exception-in-subbing ---
[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-throwing-exception-in-subbing ---
[INFO] Changes detected - recompiling the module!
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ mockito-throwing-exception-in-subbing ---
[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-throwing-exception-in-subbing ---
[INFO] Changes detected - recompiling the module!
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ mockito-throwing-exception-in-subbing ---
-------------------------------------------------------
T E S T S
-------------------------------------------------------
Running com.logicbig.example.ProcessorTest
-- exception thrown --
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.888 sec
Results :
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 5.793 s
[INFO] Finished at: 2020-05-13T00:29:01-05:00
[INFO] ------------------------------------------------------------------------
Note that if we try to throw checked exception in above example i.e.
Mockito.when(myService.doSomething()).thenThrow(new Exception("Cannot process"));
then we will have following runtime exception:
org.mockito.exceptions.base.MockitoException:
Checked exception is invalid for this method!
Invalid: java.lang.Exception: Cannot process
at com.logicbig.example.ProcessorTest.processTest(ProcessorTest.java:13)
Testing checked exception
package com.logicbig.example;
import junit.framework.TestCase;
import org.junit.Assert;
import org.junit.Test;
import org.mockito.Mockito;
public class ProcessorTest2 {
@Test
public void processTest() throws Exception {
MyService myService = Mockito.mock(MyService.class);
Mockito.when(myService.doSomething2()).thenThrow(new Exception("Cannot process"));
MyProcessor myProcessor = new MyProcessor(myService);
try {
String returnedValue = myProcessor.process2();
TestCase.fail();
}catch (Throwable e){
System.out.println("-- exception thrown --");
Assert.assertTrue(e instanceof Exception);
Assert.assertEquals(e.getMessage(), "Cannot process");
}
}
}
D:\mockito-throwing-exception-in-subbing>mvn test -Dtest="ProcessorTest2"
[INFO] Scanning for projects...
[INFO]
[INFO] -----< com.logicbig.example:mockito-throwing-exception-in-subbing >-----
[INFO] Building mockito-throwing-exception-in-subbing 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ mockito-throwing-exception-in-subbing ---
[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-throwing-exception-in-subbing ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ mockito-throwing-exception-in-subbing ---
[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-throwing-exception-in-subbing ---
[INFO] Changes detected - recompiling the module!
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ mockito-throwing-exception-in-subbing ---
-------------------------------------------------------
T E S T S
-------------------------------------------------------
Running com.logicbig.example.ProcessorTest2
-- exception thrown --
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 1.312 sec
Results :
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 5.591 s
[INFO] Finished at: 2020-05-13T00:35:38-05:00
[INFO] ------------------------------------------------------------------------
Testing handled exception
public class ProcessorTest3 {
@Test
public void processTest() throws Exception {
MyService myService = Mockito.mock(MyService.class);
Mockito.when(myService.doSomething2()).thenThrow(new Exception("Cannot process"));
MyProcessor myProcessor = new MyProcessor(myService);
String returnedValue = myProcessor.process3();
Assert.assertEquals(returnedValue, "default-value");
}
}
D:\mockito-throwing-exception-in-subbing>mvn test -Dtest="ProcessorTest3"
[INFO] Scanning for projects...
[INFO]
[INFO] -----< com.logicbig.example:mockito-throwing-exception-in-subbing >-----
[INFO] Building mockito-throwing-exception-in-subbing 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ mockito-throwing-exception-in-subbing ---
[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-throwing-exception-in-subbing ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ mockito-throwing-exception-in-subbing ---
[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-throwing-exception-in-subbing ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ mockito-throwing-exception-in-subbing ---
-------------------------------------------------------
T E S T S
-------------------------------------------------------
Running com.logicbig.example.ProcessorTest3
-- exception thrown in MyProcess --
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.757 sec
Results :
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.830 s
[INFO] Finished at: 2020-05-13T00:36:36-05:00
[INFO] ------------------------------------------------------------------------
Using doThrow-when method
package com.logicbig.example;
import junit.framework.TestCase;
import org.junit.Assert;
import org.junit.Test;
import org.mockito.Mockito;
public class ProcessorTest4 {
@Test
public void processTest() {
MyService myService = Mockito.mock(MyService.class);
Mockito.doThrow(new RuntimeException("Cannot process")).when(myService).doSomething();
MyProcessor myProcessor = new MyProcessor(myService);
try {
String returnedValue = myProcessor.process();
TestCase.fail();
}catch (Exception e){
System.out.println("-- exception thrown --");
Assert.assertTrue(e instanceof RuntimeException);
Assert.assertEquals(e.getMessage(), "Cannot process");
}
}
}
D:\mockito-throwing-exception-in-subbing>mvn test -Dtest="ProcessorTest4"
[INFO] Scanning for projects...
[INFO]
[INFO] -----< com.logicbig.example:mockito-throwing-exception-in-subbing >-----
[INFO] Building mockito-throwing-exception-in-subbing 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ mockito-throwing-exception-in-subbing ---
[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-throwing-exception-in-subbing ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ mockito-throwing-exception-in-subbing ---
[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-throwing-exception-in-subbing ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ mockito-throwing-exception-in-subbing ---
-------------------------------------------------------
T E S T S
-------------------------------------------------------
Running com.logicbig.example.ProcessorTest4
-- exception thrown --
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.861 sec
Results :
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.656 s
[INFO] Finished at: 2020-05-13T00:37:35-05:00
[INFO] ------------------------------------------------------------------------
We should use doThrow() when we want to stub the void method with an exception.
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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