Techniques for testing software applications in stack-based computing environments are discussed. A tested application is executed at predetermined logical positions in a stack, such as at a layer of the OSI reference model. An expected result of an operation performed by the application is identified. A first set of computer-executable instructions is installed at a first position logically above the tested application, and a second set of computer-executable instructions is installed at a second position logically below the tested application. One or both sets of instructions simulate inputs to the application. The application is executed based on the simulated inputs, and one or both sets of instructions are used to compare outputs from the application with the expected result. Various, virtually unlimited tests can be performed on the software application without the use of extensive test infrastructure.