Software testing is one of the hardest and most expensive activities in software development. The need for test adequacy criteria is widely recognized. Several of them, together with software tools to support them, have been proposed. However, in most cases such criteria and tools aim at unit testing only. Other testing phases, like integration testing have few automatized aid. Interface Mutation is a new criterion for interprocedural test quality assessment based on mutations. This paper focuses on a testing tool named Proteum/IM that supports Interface Mutation for C programs.