Two facts about declarative programming prevent the application of conventional testing methods. First, the classical test coverage measures such as statement, branch or path coverage, cannot be used, since in declarative programs no control flow notion exists. Second, there is no widely accepted language available for formal specification, since predicate logic, which is the most common formalism for declarative programming, is already a very high-level abstract language. This paper presents a new approach exending previous work by the authors on test input generation for declarative programs. For this purpose, the existing program instrumentation notion is extended and a new logic coverage measure is introduced. The approach is mathematically formalized and the goal of achieving 100% program logic coverage controls the automatic test input generation. The method is depicted by means of logic programming; the results are, however, generally applicable. Finally, the concepts introduced have been used practically within a test environment. © 1998 John Wiley & Sons, Ltd.