How can I use Mockito to verify that a mock was never invoked using `verifynointeractions`?

General Discussions
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1

I want to ensure in my tests that a given mock has had no interactions at all. While never() works for individual methods, I need a way to verify the entire mock wasn’t used.

For example, I want to confirm that nothing was printed to System.out or System.err without verifying each method separately.

How can I achieve this with verifynointeractions in Mockito?

2

The trick with mockConstruction is that the mocked object only exists inside the try-with-resources block. For example:

try (MockedConstruction<MyClass> mocked = Mockito.mockConstruction(MyClass.class)) {
    MyClass obj = new MyClass(); // this is mocked
    Mockito.when(obj.someMethod()).thenReturn("mocked value");

    // Assertions here
}

Anything constructed outside the block won’t be mocked. Ensuring the construction happens inside the try block fixes the issue.

3

Instead of just relying on the first instance, you can inspect all objects created with mocked.constructed(). This is especially useful when multiple objects are constructed during a test:

try (MockedConstruction<MyClass> mocked = Mockito.mockConstruction(MyClass.class)) {
    MyClass obj = new MyClass(); // mocked
    List<MyClass> mocks = mocked.constructed();
    Mockito.verify(mocks.get(0)).someMethod();
}

This approach ensures that every constructed instance is properly mocked and verifiable.

4

A few things to watch out for with mockConstruction:

  • Don’t instantiate the object before the try block.

  • Only new constructions are affected; existing objects aren’t mocked.

  • Use the MockedConstruction handle to verify interactions or capture created instances.

Following these rules usually resolves the issue where the mocked object doesn’t behave as expected.