Clearly the program is of no use if the user cannot be certain that it is giving the correct results. It is therefore necessary to test the results in as many cases as possible to be as certain as possible that it is working as intended. This task is rather difficult as it is not easy to find a foolproof method of testing such a complex program since there is no way of knowing whether the line profiles it produces are correct or not. There are however several methods that can be used to test certain aspects of the program. Firstly, checking the geometry routine (which is the major new section of the program) as a separate sub-section of the program is possible. This is done in detail in section 5.1 below. Just checking the different subsections of the program is, however, not sufficient and some way of checking the final output is also necessary. There are a few special situations for spherically symmetric clouds which have an analytical solution and these are shown in section 5.2. Beyond these special cases the only way of testing the more general cases is by comparison with the output from other programs. Since the ASTRA program is based on the STEN program which has been rigorously tested over many years it is possible to compare results with this program by simulating spherically symmetric clouds. This will be done in section 5.2.3 by reproducing the results presented by Henry Buckley in his thesis [7]. His work is chosen as the models he ran are well documented and his version of the STEN program has been well tested against other programs that are not related to the STEN program. His modification to the STEN program enables the testing of the ability of the ASTRA program to cope with cloud rotation by testing the specific case of solid body rotation. Finally, there has been some theoretical work done by Richer & Padman [27] on the rotation of protostellar discs and a test of differential rotation is possible by reproducing this work in section 5.3.1. The successful reproduction of all these results provides the best confirmation that the program is indeed working as intended.