Interoperability issues between diﬀerent implementations in large-scale systems is one of the major reasons for increased eﬀort during system test. This paper addresses this problem in the context of the Online Certiﬁcate Status Protocol (OCSP) in a Public Key Infrastructure (PKI), which is part of the certiﬁcate veriﬁcation process of many components. The high interconnection of OCSP clients and server increases the complexity of system tests to ensure interoperation. This paper pro- vides a component based testing method for clients and servers using OCSP exempliﬁed by testing PKI components of a nationwide IT infrastructure. The method ensures high interoperability requirements of large-scale infrastructures during component tests and reduces eﬀorts for test execution.