This is particularly noticable with wpt which is doing (an afaik useless) clone of the repoistory that takes much longer than the 60s wait, so after selecting an option you can wait a long time and end up with a traceback about run-mozharness not being available. Possibly the wizard should just not display until all the deps are ready.
A counter argument to this is that some options (I guess in this case just Exit to Shell), don't depend on all those things. From a UX standpoint, the current setup gives developers a chance to make their choice while the download/clone happens in the background. What if after making the choice we printed, "Waiting for tests to download.." or something similar (users don't need to know that the download was already in progress).
You need to log in before you can comment on or make changes to this bug.