Add tests for the command and executable callbacks, and make them use local node_modulse esxecutables like other linters

ale_linters/less/lessc.vim

@@ -1,12 +1,25 @@
-" Author: zanona <https://github.com/zanona>
+" Author: zanona <https://github.com/zanona>, w0rp <devw0rp@gmail.com>
 " Description: This file adds support for checking Less code with lessc.
 
+call ale#Set('less_lessc_executable', 'lessc')
 call ale#Set('less_lessc_options', '')
+call ale#Set('less_lessc_use_global', 0)
+
+function! ale_linters#less#lessc#GetExecutable(buffer) abort
+    return ale#node#FindExecutable(a:buffer, 'less_lessc', [
+    \   'node_modules/.bin/lessc',
+    \])
+endfunction
 
 function! ale_linters#less#lessc#GetCommand(buffer) abort
-    return 'lessc'
-    \   . ' --no-color --lint --include-path=' . expand('%:p:h')
-    \   . ' ' . ale#Var(a:buffer, 'less_lessc_options')
+    let l:executable = ale_linters#less#lessc#GetExecutable(a:buffer)
+    let l:dir = expand('#' . a:buffer . ':p:h')
+    let l:options = ale#Var(a:buffer, 'less_lessc_options')
+
+    return ale#Escape(l:executable)
+    \   . ' --no-color --lint'
+    \   . ' --include-path=' . ale#Escape(l:dir)
+    \   . (!empty(l:options) ? ' ' . l:options : '')
     \   . ' -'
 endfunction
 
@@ -29,8 +42,8 @@ endfunction
 
 call ale#linter#Define('less', {
 \   'name': 'lessc',
-\   'executable': 'lessc',
-\   'output_stream': 'stderr',
+\   'executable_callback': 'ale_linters#less#lessc#GetExecutable',
 \   'command_callback': 'ale_linters#less#lessc#GetCommand',
 \   'callback': 'ale_linters#less#lessc#Handle',
+\   'output_stream': 'stderr',
 \})