Question

I would like to write a Unit Test for a (rather complex) Bash completion script, preferrably with Python – just something that gets the values of a Bash completion programmatically.
The test should look like this:

def test_completion():
  # trigger_completion should return what a user should get on triggering 
  # Bash completion like this: 'pbt createkvm<TAB>' 
  assert trigger_completion('pbt createkvm') == "module1 module2 module3" 

How can I simulate Bash completion programmatically to check the completion values inside a testsuite for my tool?

Answer 1

Say you have a bash-completion script in a file called asdf-completion, containing:

_asdf() {
COMPREPLY=()
local cur prev
cur=$(_get_cword)
COMPREPLY=( $( compgen -W "one two three four five six" -- "$cur") )
return 0
}    
complete -F _asdf asdf

This uses the shell function _asdf to provide completions for the fictional asdf command. If we set the right environment variables (from the bash man page), then we can get the same result, which is the placement of the potential expansions into the COMPREPLY variable. Here’s an example of doing that in a unittest:

import subprocess
import unittest

class BashTestCase(unittest.TestCase):
    def test_complete(self):
        completion_file="asdf-completion"
        partial_word="f"
        cmd=["asdf", "other", "arguments", partial_word]
        cmdline = ' '.join(cmd)

        out = subprocess.Popen(['bash', '-i', '-c',
            r'source {compfile}; COMP_LINE="{cmdline}" COMP_WORDS=({cmdline}) COMP_CWORD={cword} COMP_POINT={cmdlen} $(complete -p {cmd} | sed "s/.*-F \\([^ ]*\\) .*/\\1/") && echo ${{COMPREPLY[*]}}'.format(
                compfile=completion_file, cmdline=cmdline, cmdlen=len(cmdline), cmd=cmd[0], cword=cmd.index(partial_word)
                )],
            stdout=subprocess.PIPE)
        stdout, stderr = out.communicate()
        self.assertEqual(stdout, "four five\n")

if (__name__=='__main__'):
    unittest.main()

This should work for any completions that use -F, but may work for others as well.

je4d’s comment to use expect is a good one for a more complete test.