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eyeball

eyeball is a tiny bash script that helps you detect and understand changes in a program's output.

It can sometimes be used as a cheap and cheerful alternative to writing test code.

Quick start

Run a test of your program python noodles.py --extra-soy for the first time, recording the output (stdout+stderr) in noodles.out as well as displaying it on your console.

Remember the double quotes around your command if it contains spaces!

eyeball "python noodles.py --extra-soy" noodles.out

Run the test again (usually afer a code change is made) using the same command as above. If the new output exactly matches the baseline output, eyeball reports a PASS.

Otherwise, eyeball reports a FAIL and displays a diff between the new and baseline output and the new output is stored in noodles.out.eyeball.

If the difference in output is expected, you can update the baseline:

eyeball --update noodles.out

Otherwise, fix the bug in noodles.py and try again!

Installation

To install, simply copy the eyeball script somehere on your PATH, e.g. /usr/local/bin.

Diff command

  • If git is installed, eyeball uses git --no-pager diff --color-words --no-index to generate a lovely colourised word-by-word diff report.
  • If git is not installed, eyeball uses plain old diff.
  • The diff command can be customised by setting the EYEBALL_DIFF environment variable, e.g. export EYEBALL_DIFF=colordiff

Notes and tips

  • The output of your program needs to be deterministic for an eyeball test to work. Hopefully you can control the output in most circumstances (seeding dates, random number generators etc). However if you need to do further processing on the output you can pipe it to sed or awk for example: eyeball "blah.sh | sed sed 's/date is .*/date is DATE/'" blah.out
  • If your program writes output to file(s), simply output the file contents as part of the command, e.g. eyeball "gen-stuff.sh; cat stuff1.json; cat stuff2.txt" gen-stuff.out.

Testing

Run ./eyeball ./test.sh test.out