A method for testing an application that invokes an application programming interface (API) comprises identifying signatures for APIs. A package associated with the API is identified in the application under test, and a package name of the API is identified in the signatures. During runtime of the application under test, request and response objects (or other objects) for the identified package are created using the package name and reflection. The created request object is then used to invoke the API to test the application under test and the response object is used to evaluate the response with expected response.