How can I tell if an object is a Mockito mock?

As a follow up, the Mockito public API now has this method:

MockingDetails org.mockito.Mockito.mockingDetails(Object toInspect)

Which is the result of the issue that @David Wallace raised. The returned object supports the methods isMock() as well as isSpy() along with a few other methods that provide additional mocking information.

Looks like there is no such API (please raise an issue, it should be!) Fortunately (following your comment below) there is a method in the org.mockito.internal.util package:

import org.mockito.internal.util.MockUtil;

new MockUtil().isMock(obj)

In the future Mockito.isMock() method might be added to public API, see: Issue 313: Provide isMock outside of org.mockito.internal).