I am unsure on how to mock an enum singleton class.
public enum SingletonObject{
INSTANCE;
private int num;
protected setNum(int num) {
this.num = num;
}
public int getNum() {
return num;
}
I'd like to stub getNum() in the above example, but I can't figure out how to mock the actual SingletonObject class. I thought using Powermock to prepare the test would help since enums are inherently final.
//... rest of test code
@Test
public void test() {
PowerMockito.mock(SingletonObject.class);
when(SingletonObject.INSTANCE.getNum()).thenReturn(1); //does not work
}
This is using PowerMockMockito 1.4.10 and Mockito 1.8.5.
If you want to stub out what INSTANCE returns, you can do it but it's kind of nasty (using reflection & bytecode manipulation). I created & tested a simple project with three classes using the PowerMock 1.4.12 / Mockito 1.9.0. All classes were in the same package.
public enum SingletonObject {
INSTANCE;
private int num;
protected void setNum(int num) {
this.num = num;
}
public int getNum() {
return num;
}
}
public class SingletonConsumer {
public String consumeSingletonObject() {
return String.valueOf(SingletonObject.INSTANCE.getNum());
}
}
import static org.junit.Assert.*;
import static org.powermock.api.mockito.PowerMockito.*;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
import org.powermock.reflect.Whitebox;
@RunWith(PowerMockRunner.class)
@PrepareForTest({SingletonObject.class})
public class SingletonConsumerTest {
@Test
public void testConsumeSingletonObject() throws Exception {
SingletonObject mockInstance = mock(SingletonObject.class);
Whitebox.setInternalState(SingletonObject.class, "INSTANCE", mockInstance);
when(mockInstance.getNum()).thenReturn(42);
assertEquals("42", new SingletonConsumer().consumeSingletonObject());
}
}
The call to the Whitebox.setInternalState
replaces INSTANCE
with a mock object that you can manipulate within your test.
Have an interface with the methods you intend to mock
public interface SingletonInterface {
int getNum();
}
Let the enum implement the interface
public enum SingletonObject implements SingletonInterface {
INSTANCE;
private int num;
protected void setNum(int num) {
this.num = num;
}
@Override
public int getNum() {
return num;
}
}
Mock the interface
@Test
public void test() {
SingletonInterface singleton = Mockito.mock(SingletonInterface.class);
when(singleton.getNum()).thenReturn(1); //does work
}
In addition to above Matt Lachman answer, create a object factory for power mock in SingleTonConsumerTest.class
@ObjectFactory
public IObjectFactory getObjectFactory() {
return new org.powermock.modules.testng.PowerMockObjectFactory();
}
This will remove Mockito cannot mock/spy following: - final classes - anonymous classes - primitive types
error.
I am not sure if this is best approach, but in my case it's working without troubles so far. I am using mockito-core and mockito-inline (3.11.0) and I am mocking my singleton with help of spy. Example with your class:
SingletonObject so = SingletonObject.INSTANCE;
private SingletonObject spySo = Mockito.spy(so);
@Before
public void setUp() {
Mockito.doReturn(10).when(spySo).getNum();
}
@Test
public void simpleTest() {
assertThat(spySo.getNum(), is(10));
}
Mockito docs are not explicit on enum use case:
Powermock support:
build.gradle ( ** should work with Maven too)
testImplementation 'org.junit.jupiter:junit-jupiter-api:5.8.1'
testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.8.1'
testImplementation 'org.mockito:mockito-inline:4.0.0'
testImplementation 'org.mockito:mockito-junit-jupiter:4.1.0'
As of the available experimental features ( Powermock + JUnit 5 ), can give a try to:
implementation group: 'org.powermock', name: 'powermock-module-junit5', version: '1.6.4'
testImplementation 'org.powermock:powermock-mockito-release-full:1.6.4'
Enum:
public enum ConnectionFactory {
INSTANCE;
public Connection get() throws SQLException {
//
// Load url from configuration file ('application.yml')
//
final var connection = DriverManager.getConnection(url);
connection.setAutoCommit(false);
return connection;
}
}
Can use these approaches:
class DatabaseUnitTests {
private final ConnectionFactory connectionFactory = Mockito.spy(ConnectionFactory.INSTANCE);
//Or
@InjectMocks
private final ConnectionFactory connectionFactory = Mockito.mock(ConnectionFactory.class);
@Test
void check_is_database_connection_is_OK(){
Mockito.doReturn(mockedConnection()).when(connectionFactory).get();
// Do something
}
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.