[joelbluminator]

OK. first I could be ignorant about Java since I haven't touched it in more than a decade. Which library is doing that? And also what is mock(User.java) returning - is it an actual User instance or a stub? I want a real User instance (nothing mocked in it) with just the one method mocked.

And again if this is possible I will admit ignorance and tip my hat at the Java guys.

[hota_mazi]

It's Mockito [1], which has been a standard for a while. There are other libraries and they use different strategies to provide this kind of functionalities (dynamic proxies, bytecode weaving, annotation processing, etc...).

[1] https://site.mockito.org/

[joelbluminator]

And ... is the whole user being mocked or just the method?

[vincnetas]

It creates a stub, but you can also configure it to pass any method calls to original implementation. You should be tiping your hat i think.

https://javadoc.io/static/org.mockito/mockito-core/3.11.2/or...

User mock = mock(User.java)

Should have been

User mock = mock(User.class)

[hota_mazi]

Ah oops, I've been writing exclusively Kotlin for several years, my Java is becoming rusty (no pun intended).

[throwaway_fjmr]

I think what you want is a "spy" (partial mock), not a full "mock", but yes, both are possible. You can partially mock classes, i.e., specific methods only. Syntax is almost the same, instead of mock(User.class) you write spy(User.class).