mockito, how to coverage test the catch block

Question

Android app, Having a function calling another function, that function may throw

static string SOME_DEFINE_1 = "some_define_1";
......
void myFunc() {
        try {
            HashMap<String, String> data = new HashMap<>();
            data.put("key_1", SOME_DEFINE_1);
            otherObject.func(data);
        } catch (Throwable ex){
            Log.e(TAG, "+++ exception from otherObject.func(), "+ ex.toString());
            // do something
            anotherFunc();
        }
    }

How to test the catch block is called when unit testing the myFunc?

Answer 1

It isn't clear in your example where otherObject comes from, but in general, to test the exception handling blocks you need code that will throw the exception. In this example, one way may be to mock the otherObject and then use thenThrow to cause it to throw an exception when the func(data) method is called. You could use a spy of the class you are testing and stub the anotherFunc method so you can replace it with something else and then verify if it was invoked for the conditions you expect to throw the exception.

These articles show the general approach:

• https://www.baeldung.com/mockito-spy - (number 4)
• https://www.baeldung.com/mockito-exceptions

So in a pseudo-code example:

// arrange
myClassUnderTest = spy(TheClassUnderTest);
otherObject = mock(OtherObject);
doNothing().when(myClassUnderTest).anotherFunc();
doThrow(new RuntimeException("simulated exception")).when(otherObject).func(any());

// act
myClassUnderTest.myFunc();

// assert
verify(myClassUnderTest , times(1)).anotherFunc();