1. A method comprises: receiving application requirements; receiving a plurality of implementation results of application code as the application code is being developed in one or more phases; and testing the plurality of implementation results of the application code as the application code is being developed based on the application requirements, wherein, for a current implementation result of the plurality of implementation results, the testing includes: generating at least one test case based on one or more of the application requirements; stimulating the current implementation result based on the at least one test case to produce a current application system response; comparing observed behavior of the current application system response with prescribed behavior of the at least one test case; and generating feedback based on the comparing of the observed behavior of the current application system response with the prescribed behavior of the at least one test case.