Before: Save g:ale_python_mypy_executable Save g:ale_python_mypy_options Save g:ale_python_mypy_use_global unlet! g:ale_python_mypy_executable unlet! g:ale_python_mypy_options unlet! g:ale_python_mypy_use_global let b:bin_dir = has('win32') ? 'Scripts' : 'bin' runtime ale_linters/python/mypy.vim call ale#test#SetDirectory('/testplugin/test/command_callback') call ale#test#SetFilename('test.py') After: Restore unlet! b:bin_dir unlet! b:executable call ale#test#RestoreDirectory() call ale#linter#Reset() Execute(The mypy callbacks should return the correct default values): AssertEqual \ 'mypy', \ ale_linters#python#mypy#GetExecutable(bufnr('')) AssertEqual \ 'cd ' . ale#Escape(g:dir) . ' && ' . ale#Escape('mypy') \ . ' --show-column-numbers ' \ . '--shadow-file %s %t %s', \ ale_linters#python#mypy#GetCommand(bufnr('')) Execute(The mypy executable should be configurable, and escaped properly): let g:ale_python_mypy_executable = 'executable with spaces' AssertEqual \ 'executable with spaces', \ ale_linters#python#mypy#GetExecutable(bufnr('')) AssertEqual \ 'cd ' . ale#Escape(g:dir) . ' && ' . ale#Escape('executable with spaces') \ . ' --show-column-numbers ' \ . '--shadow-file %s %t %s', \ ale_linters#python#mypy#GetCommand(bufnr('')) Execute(The mypy command callback should let you set options): let g:ale_python_mypy_options = '--some-option' AssertEqual \ 'cd ' . ale#Escape(g:dir) . ' && ' . ale#Escape('mypy') \ . ' --show-column-numbers --some-option ' \ . '--shadow-file %s %t %s', \ ale_linters#python#mypy#GetCommand(bufnr('')) Execute(The mypy command should switch directories to the detected project root): silent execute 'file ' . fnameescape(g:dir . '/python_paths/no_virtualenv/subdir/foo/bar.py') AssertEqual \ 'mypy', \ ale_linters#python#mypy#GetExecutable(bufnr('')) AssertEqual \ 'cd ' . ale#Escape(ale#path#Simplify(g:dir . '/python_paths/no_virtualenv/subdir')) \ . ' && ' . ale#Escape('mypy') \ . ' --show-column-numbers ' \ . '--shadow-file %s %t %s', \ ale_linters#python#mypy#GetCommand(bufnr('')) Execute(The mypy callbacks should detect virtualenv directories and switch to the project root): silent execute 'file ' . fnameescape(g:dir . '/python_paths/with_virtualenv/subdir/foo/bar.py') let b:executable = ale#path#Simplify(g:dir . '/python_paths/with_virtualenv/env/' . b:bin_dir . '/mypy') AssertEqual \ b:executable, \ ale_linters#python#mypy#GetExecutable(bufnr('')) AssertEqual \ 'cd ' . ale#Escape(ale#path#Simplify(g:dir . '/python_paths/with_virtualenv/subdir')) \ . ' && ' . ale#Escape(b:executable) \ . ' --show-column-numbers ' \ . '--shadow-file %s %t %s', \ ale_linters#python#mypy#GetCommand(bufnr('')) Execute(You should able able to use the global mypy instead): silent execute 'file ' . fnameescape(g:dir . '/python_paths/with_virtualenv/subdir/foo/bar.py') let g:ale_python_mypy_use_global = 1 AssertEqual \ 'mypy', \ ale_linters#python#mypy#GetExecutable(bufnr('')) AssertEqual \ 'cd ' . ale#Escape(ale#path#Simplify(g:dir . '/python_paths/with_virtualenv/subdir')) \ . ' && ' . ale#Escape('mypy') \ . ' --show-column-numbers ' \ . '--shadow-file %s %t %s', \ ale_linters#python#mypy#GetCommand(bufnr(''))