In this paper we present the theory for evaluating the test error that we commit when we replace a standard analog test by a lower-cost alternative measurement. The evaluation takes place during the design and test development phases and relies on a tractable number of simulations. The test error is expressed in terms of test escape and yield loss which are estimated in parts per million accuracy. The theory is demonstrated with an example. In particular, we evaluate whether a dedicated on-chip envelope detector can be used to eliminate the NF test for an LNA.