Before: call ale#assert#SetUpLinterTest('python', 'prospector') After: call ale#assert#TearDownLinterTest() Execute(Setting executable to 'pipenv' appends 'run prospector'): let g:ale_python_prospector_executable = 'path/to/pipenv' AssertLinter 'path/to/pipenv', \ ale#Escape('path/to/pipenv') . ' run prospector' \ . ' --messages-only --absolute-paths --zero-exit --output-format json %s' Execute(Pipenv is detected when python_prospector_auto_pipenv is set): let g:ale_python_prospector_auto_pipenv = 1 call ale#test#SetFilename('/testplugin/test/python_fixtures/pipenv/whatever.py') AssertLinter 'pipenv', \ ale#Escape('pipenv') . ' run prospector' \ . ' --messages-only --absolute-paths --zero-exit --output-format json %s'