Before: Save g:ale_cs_mcsc_source unlet! g:ale_cs_mcsc_source runtime ale_linters/cs/mcsc.vim After: unlet! g:ale_cs_mcsc_source call ale#linter#Reset() Execute(The mcs handler should work with the default of the buffer's directory): AssertEqual \ [ \ { \ 'lnum': 12, \ 'col' : 29, \ 'text': '; expected', \ 'code': 'CS1001', \ 'type': 'E', \ 'filename': ale#path#Simplify(expand('%:p:h') . '/Test.cs'), \ }, \ ], \ ale_linters#cs#mcsc#Handle(347, [ \ 'Test.cs(12,29): error CS1001: ; expected', \ 'Compilation failed: 2 error(s), 1 warnings', \ ]) Execute(The mcs handler should handle cannot find symbol errors): let g:ale_cs_mcsc_source = '/home/foo/project/bar' AssertEqual \ [ \ { \ 'lnum': 12, \ 'col' : 29, \ 'text': '; expected', \ 'code': 'CS1001', \ 'type': 'E', \ 'filename': ale#path#Simplify('/home/foo/project/bar/Test.cs'), \ }, \ { \ 'lnum': 101, \ 'col': 0, \ 'text': 'Unexpected processor directive (no #if for this #endif)', \ 'code': 'CS1028', \ 'type': 'E', \ 'filename': ale#path#Simplify('/home/foo/project/bar/Test.cs'), \ }, \ { \ 'lnum': 10, \ 'col': 12, \ 'text': 'some warning', \ 'code': 'CS0123', \ 'type': 'W', \ 'filename': ale#path#Simplify('/home/foo/project/bar/Test.cs'), \ }, \ ], \ ale_linters#cs#mcsc#Handle(347, [ \ 'Test.cs(12,29): error CS1001: ; expected', \ 'Test.cs(101,0): error CS1028: Unexpected processor directive (no #if for this #endif)', \ 'Test.cs(10,12): warning CS0123: some warning', \ 'Compilation failed: 2 error(s), 1 warnings', \ ])