InvalidUseOfMatchersException when using mockito to force a CloneNotSupportedException in a Copy() method being junit tested

Question

I'm trying to access part of a copy method protected by a try catch using mockito while attempting to get 100% coverage in my junit tests. The class that contains the method I want to access implements cloneable making it difficult to throw ClassNotFoundExceptions.

I've tried to force this exception several different ways through mockito's ability to throw exceptions when calling a method but have always come up with an InvalidUseOfMatchersException.

following is the code i need to access and my best attempt at reaching it, respectively

catch(ClassNotFoundException cnfe) {
            cnfe.printStackTrace();
}

MyClass dict = mock(MyClass.class);
Object obj1 = new Object();

when(MyClass.copy(anyObject())).thenThrow(ClassNotFoundException.class);
dict.copy(obj1);

I expect to reach the cnfe.printStackTrace() line but cannot.

The same question applies to a clone method I in which I need to throw a clonenotsupportedexception — dead.frank, Jun 18 '19 at 13:53
You want to throw a ClassNotFoundException, but actually you are throwing a CloneNotSupportedException. — Maxime Launois, Jun 18 '19 at 13:54
@MaximeLaunois mistakenly typed - thank you but error persists — dead.frank, Jun 18 '19 at 14:01

Maxime Launois · Accepted Answer · 2019-07-02T16:24:00.237

You seem to be mocking a static method, which is actually impossible. According to @Matthias, it would require modifying the class' byte code at runtime.

You must always call when with an instance method call because:

This guarantees that the method will be called on the mock and not on the original class (i.e. MyClass).
This prevents compile-time errors because such non-static methods cannot be referenced from a static context.

Here is the full Java code:

try {
    MyClass dict = mock(MyClass.class);
    Object obj1 = new Object();

    when(dict.copy(anyObject())).thenThrow(ClassNotFoundException.class);
    dict.copy(obj1);
} catch (ClassNotFoundException ex) {
    ex.printStackTrace();
}

This should output:

Exception in thread "main" java.lang.ClassNotFoundException

InvalidUseOfMatchersException when using mockito to force a CloneNotSupportedException in a Copy() method being junit tested

1 Answers1