How to Force a Method to Throw an Exception in Junit Testing

How to force a method to throw an Exception in jUnit testing?

You need to first mock the class containing selectSomethingBySomething() and then record this behavior. In mockito you'll say:

SomeDao someDaoMock = mock(SomeDao.class);

willThrow(new SQLException())).given(someDaoMock).selectSomethingBySomething();

Then inject someDaoMock into your class under test and when it calls someDaoMock.selectSomethingBySomething() it'll throw previously chosen exception.

JUnit Test : Forcing exception from internal method call

As you suggested, Mockito would be a classic tool for such a usecase:

// Initialization - should probably be in the @Before method:
A a = Mockito.spy(new A());
Mockito.doThrow(new SomeException("yay!")).when(a).m2();

// Actual test:
SomeResult actualResult = a.m1();
assertEquals(someExpectedResult, actualResult); // or some other assertion

The above snippet creates a spyied object (think of it as an anonymous class that extends A) with the defined behavior that when m2() is called, a SomeException will be thrown.
Then the code goes on to call the real m1() method, which itself calls m2(), and has to handle the exception.

Junit Force to throw Exception on method call

When writing spring-boot integration test you should inject the mock beans using @MockBean annotation

@RunWith(SpringRunner.class)
@SpringBootTest(classes = Application.class, webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
@TestInstance(TestInstance.Lifecycle.PER_CLASS)
Class ATest {

    @Autowired
    private A obj;

    @MockBean
    private SimpleJdbcCall simpleJdbcCall;

    @Test
    public void throwExceptionFromMethod() {


   
    try {
       
        Mockito.when(simpleJdbcCall.withProcedureName(Mockito.anyString())).thenReturn(simpleJdbcCall);
        Mockito.when(simpleJdbcCall.declareParameters(Mockito.any())).thenReturn(simpleJdbcCall);
        Mockito.doThrow(new RuntimeException()).when(simpleJdbcCall).execute( 
        ArgumentMatchers.any(SqlParameterSource.class)); 

        //or you can use thenThrow also

        Mockito.when(simpleJdbcCall.execute(ArgumentMatchers.any(SqlParameterSource.class))).thenThrow(RuntimeException.class);

        final int message = obj.mymeth(modifyLeadDispositionRequest);
        
    } catch (Exception e) {
        e.printStackTrace();
       // just to assert here 
    }
  }
}

You can a follow some of the examples here for testing exceptions in junit4 or junit5

How do you assert that a certain exception is thrown in JUnit tests?

It depends on the JUnit version and what assert libraries you use.

• For JUnit5 and 4.13 see answer https://stackoverflow.com/a/2935935/2986984
• If you use assertJ or google-truth, see answer https://stackoverflow.com/a/41019785/2986984

The original answer for JUnit <= 4.12 was:

@Test(expected = IndexOutOfBoundsException.class)
public void testIndexOutOfBoundsException() {

    ArrayList emptyList = new ArrayList();
    Object o = emptyList.get(0);

}

Though answer https://stackoverflow.com/a/31826781/2986984 has more options for JUnit <= 4.12.

Reference :

• JUnit Test-FAQ

How to simulate throwing an exception only once in retry with JUnit/Mockito test?

According to the Mockito documentation you can set different behavior for consecutive method calls.

when(mock.someMethod("some arg"))
    .thenThrow(new RuntimeException())
    .thenReturn("foo");

In case of a void method you can do something similar (Mockito documentation)

doThrow(new RuntimeException())
    .doNothing()
    .when(mock).doSomething();

how to test that a method throws an exception junit5

Maybe you can try the following code:

@Test
public void tryThrowExceptionForInvalidRequest() throws Exception {

    final String invalid = "Este es un request invalido";

    InvalidInputRequestType exceptionThrown = Assertions.assertThrows(
                InvalidInputRequestType.class,
                () -> { 
                    detector.detectForRequest(invalid); 
                }
        );
    assertEquals(invalid, exceptionThrown.getMessage());
} 

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