Define an integration test

[rouson]

• Convert the original main program into a function that returns a result for comparison to the new code. The result would probably be declared something like double precision, allocatable :: positions(:,:,:), which would be allocated to shape [ncells, npositions, 3], where 3 is the number of spatial directions and where positions(:,:,1) holds x values, positions(:,:,2) holds y values, and positions(:,:,3) holds z values.
• TBD: we can discuss in an upcoming call how best to compare the function result with that of the new code.

[rouson]

I think PR #92 addresses this so I'll close this issue. @davytorres feel free to reopen it if I'm mistaken.