Testing ClassNotFound Exception

Question

I'm trying to test that a class is not found with UnitTest on Android.

What's going on:
1. I'm writing an android library with transitive dependencies which are resolved in the host application
2. The developer may remove some dependencies for example remove all com.example.package
3. I have a Factory that will try to instantiate (using reflection) an Object and catch the ClassNotFoundException. If the developer remove the dependencies, the exception should be thrown.
4. I want to test this case, but all I found is issue with dependencies, not how to test for it.

Example code I want to test

try {
    sNetworkResponseBuilderClass = OkHttpNetworkResponse.Builder.class;
} catch (Exception e){
    // <<<< I want to test this case
    new ClassNotFoundException("Unable to find OkHttpNetworkResponse.Builder.class").printStackTrace();
    return null;
}

library used: hamcrast, mockito, JUnit 4.

Do you know how to do it?

Answer 1

So for me the first thing you need to do is to extract the part of the code that can throw a ClassNotFoundException in order to be able to easily mock it, something like:

public Class<? extends NetworkResponseBuilder> getNetworkResponseBuilderClass()
    throws ClassNotFoundException {
    // Your logic here
}

Then you can test a real factory instance using Mockito.spy to be able to redefine the behavior of the method getNetworkResponseBuilderClass() as next:

public void testFactoryIfNetworkResponseBuilderNotFound() {
    Factory factory = spy(new Factory());
    when(factory.getNetworkResponseBuilderClass()).thenThrow(
        new ClassNotFoundException()
    );
    // The rest of your test here
}

public void testFactoryIfNetworkResponseBuilderFound() {
    Factory factory = spy(new Factory());
    when(factory.getNetworkResponseBuilderClass()).thenReturn(
        OkHttpNetworkResponse.Builder.class
    );
    // The rest of your test here
}

More details about Mockito.spy.

Answer 2

Not quite sure if I understood your question correctly, but you can check with JUnit if an exception gets thrown:

@Test(expected=ClassNotFoundException.class)
public void testClassNotFoundException() {
    // a case where the exception gets thrown
}