Question

I’m trying to figure out how to test-drive software that launches external processes that take file paths as an input and write output after lengthy processing to stdout or some file? Is there some common patterns on writing tests in this kind of situations? It is hard to create fast executing tests that could verify correct usage of external tools without launching actual tools in tests and inspecting the results.

Answer 1

You could memoize (http://en.wikipedia.org/wiki/Memoization) the external processes. Write a wrapper in Ruby that computes the md5 sum of the input file and checks it against a database of known checksums. If it matches one, copy over the right output; otherwise, invoke the tool normally.