This paper presents an automatic trace-based unit testing approach to test object-oriented programs. Most automated testing tools test a class C by testing each of its methods in isolation. Such an approach works poorly if specifications are only partial, which is usually the case in practice. In contrast, our approach generates sequences of calls to the methods of C that are checked on-the-fly. This is more interactive, and has the side effect that methods are checking each other. Although simple, it seems to work quite well, even when specifications are only partially provided. We implement the approach in a tool called T2. It targets Java. It can test internal errors, Hoare triple specifications, class invariant, and even temporal properties. Furthermore, T2 accepts ’in-code’ specifications, these are specifications written in the specified class itself, and are written in plain Java; hence reducing the cost usually needed to maintain specifications to minimum.