Before: call ale#assert#SetUpFixerTest('python', 'isort') let b:bin_dir = has('win32') ? 'Scripts' : 'bin' After: call ale#assert#TearDownFixerTest() unlet! g:dir unlet! b:bin_dir Execute(The isort callback should return the correct default values): AssertEqual \ 0, \ ale#fixers#isort#Fix(bufnr('')) silent execute 'file ' . fnameescape(g:dir . '/../test-files/python/with_virtualenv/subdir/foo/bar.py') AssertEqual \ { \ 'cwd': '%s:h', \ 'command': ale#Escape(ale#path#Simplify(g:dir . '/../test-files/python/with_virtualenv/env/' . b:bin_dir . '/isort')) . ' --filename %s' . ' -', \ }, \ ale#fixers#isort#Fix(bufnr('')) Execute(The isort callback should respect custom options): let g:ale_python_isort_options = '--multi-line=3 --trailing-comma' AssertEqual \ 0, \ ale#fixers#isort#Fix(bufnr('')) silent execute 'file ' . fnameescape(g:dir . '/../test-files/python/with_virtualenv/subdir/foo/bar.py') AssertEqual \ { \ 'cwd': '%s:h', \ 'command': ale#Escape(ale#path#Simplify(g:dir . '/../test-files/python/with_virtualenv/env/' . b:bin_dir . '/isort')) \ . ' --filename %s' . ' --multi-line=3 --trailing-comma -', \ }, \ ale#fixers#isort#Fix(bufnr('')) Execute(Pipenv is detected when python_isort_auto_pipenv is set): let g:ale_python_isort_auto_pipenv = 1 call ale#test#SetFilename('../test-files/python/pipenv/whatever.py') AssertEqual \ { \ 'cwd': '%s:h', \ 'command': ale#Escape('pipenv') . ' run isort' . ' --filename %s' . ' -' \ }, \ ale#fixers#isort#Fix(bufnr(''))