Signal Processing and FFT

I am trying to write a a MATLABfunction that implements a non-power-of-two FFT using power-of-two FFT’s, according to the method in which the FFT is transformed into a convolution problem. I tried using the MATLAB FFT to implement the required convolution, as long as it is called so that it computes a power-of-two FFT. how can I demonstrate with code using a random input signal input signal that my function yields the same result as the MATLAB fft() function. Then I compare the timing on a random sequence of length 999,983 to the MATLAB FFT. (x = randn(1,999983);). Any help with that please