Unfortunately, the integrated verification portion of the "Generate" step in the app does not currently support workflows containing automated fixed-point conversion. As the code generated for the converted fixed-point code does not use the original floating-point types, it is not expected to work with unmodified test benches that invoke the functions with floating-point data.
However, the automated fixed-point conversion process does produce a secondary output that is best described as a "wrapper" function that wraps the fixed-point version of the function with additional type conversion logic. This can possibly be used as part of a workaround for app limitations in the verification area. In this case, it is easiest to use the wrapper function as part of a second MATLAB Coder project.
Please see the details I posted in response to your other question regarding example main generation as the workaround will be the same. Linked here
