Better document how to run things by hand

[NicMcPhee]

There was the following question on Slack in F21:

Does anyone know of a good way to see why file_disemvowel tests are failing? They seem to give generic errors and there is no way of knowing why something crashed.

I responded with:

Probably your best bet is to

• Run file_disemvowel on a known file
• Redirect the output to some file
• Look at that file and see how it differs from what you expected

You might also find diff useful to compare your output against the expected output on the tests.

As an example, you could run:

./file_disemvowel < small_input > /tmp/our_output

followed by

diff /tmp/our_output small_output

to see how your output differed from what was expected.

Something like this should probably be in the write-up, or the "Tips & tricks" file.