Before: Save g:ale_statusline_format, g:ale_buffer_info let g:ale_buffer_info = {} " A function for conveniently creating expected count objects. function Counts(data) abort let l:res = { \ '0': 0, \ '1': 0, \ 'error': 0, \ 'warning': 0, \ 'info': 0, \ 'style_error': 0, \ 'style_warning': 0, \ 'total': 0, \} for l:key in keys(a:data) let l:res[l:key] = a:data[l:key] endfor let l:res[0] = l:res.error + l:res.style_error let l:res[1] = l:res.warning + l:res.style_warning + l:res.info let l:res.total = l:res[0] + l:res[1] return l:res endfunction After: Restore delfunction Counts Execute (Count should be 0 when data is empty): AssertEqual Counts({}), ale#statusline#Count(bufnr('%')) Execute (Count should read data from the cache): let g:ale_buffer_info = {'44': {'count': Counts({'error': 1, 'warning': 2})}} AssertEqual Counts({'error': 1, 'warning': 2}), ale#statusline#Count(44) Execute (The count should be correct after an update): let g:ale_buffer_info = {'44': {}} call ale#statusline#Update(44, []) AssertEqual Counts({}), ale#statusline#Count(44) Execute (Count should be match the loclist): let g:ale_buffer_info = { \ bufnr('%'): { \ 'loclist': [ \ { \ 'lnum': 1, \ 'bufnr': 1, \ 'vcol': 0, \ 'linter_name': 'testlinter', \ 'nr': -1, \ 'type': 'E', \ 'col': 1, \ 'text': 'Test Error', \ }, \ ], \ }, \} AssertEqual Counts({'error': 1}), ale#statusline#Count(bufnr('%')) Execute (Output should be empty for non-existant buffer): AssertEqual Counts({}), ale#statusline#Count(9001) Execute (Status() should return just errors for the old format): let g:ale_statusline_format = ['%sE', '%sW', 'OKIE'] let g:ale_buffer_info = {bufnr('%'): {}} call ale#statusline#Update(bufnr('%'), [ \ {'type': 'E'}, \ {'type': 'E', 'sub_type': 'style'}, \]) AssertEqual '2E', ale#statusline#Status() Execute (Status() should return just warnings for the old format): let g:ale_statusline_format = ['%sE', '%sW', 'OKIE'] let g:ale_buffer_info = {bufnr('%'): {}} call ale#statusline#Update(bufnr('%'), [ \ {'type': 'W'}, \ {'type': 'W', 'sub_type': 'style'}, \ {'type': 'I'}, \]) AssertEqual '3W', ale#statusline#Status() Execute (Status() should return errors and warnings for the old format): let g:ale_statusline_format = ['%sE', '%sW', 'OKIE'] let g:ale_buffer_info = {bufnr('%'): {}} call ale#statusline#Update(bufnr('%'), [ \ {'type': 'E'}, \ {'type': 'E', 'sub_type': 'style'}, \ {'type': 'W'}, \ {'type': 'W', 'sub_type': 'style'}, \ {'type': 'I'}, \]) AssertEqual '2E 3W', ale#statusline#Status() Execute (Status() should return the custom 'OK' string with the old format): let g:ale_statusline_format = ['%sE', '%sW', 'OKIE'] let g:ale_buffer_info = {bufnr('%'): {}} call ale#statusline#Update(bufnr('%'), []) AssertEqual 'OKIE', ale#statusline#Status() Execute(ale#statusline#Update shouldn't blow up when globals are undefined): unlet! g:ale_buffer_info unlet! g:ale_statusline_format call ale#statusline#Update(1, []) Execute(ale#statusline#Count should return 0 counts when globals are undefined): unlet! g:ale_buffer_info unlet! g:ale_statusline_format AssertEqual Counts({}), ale#statusline#Count(1) Execute(ale#statusline#Status should return 'OK' when globals are undefined): unlet! g:ale_buffer_info unlet! g:ale_statusline_format AssertEqual 'OK', ale#statusline#Status()