Add command callback test

ale_linters/json/jq.vim

@@ -5,7 +5,7 @@ call ale#Set('json_jq_executable', 'jq')
 function! ale_linters#json#jq#GetCommand(buffer) abort
     let l:executable = ale#Var(a:buffer, 'json_jq_executable')
 
-    return ale#Var(a:buffer, 'json_jq_executable')
+    return ale#Escape(l:executable)
 endfunction
 
 function! ale_linters#json#jq#Handle(buffer, lines) abort

test/command_callback/test_jq_command_callback.vader

@@ -0,0 +1,8 @@
+Before:
+  call ale#assert#SetUpLinterTest('json', 'jq')
+
+After:
+  call ale#assert#TearDownLinterTest()
+
+Execute(The default command should be correct):
+  AssertLinter 'jq', ale#Escape('jq')

test/test_jq_linter.vader

@@ -1,6 +1,9 @@
 Before:
   runtime ale_linters/json/jq.vim
 
+After:
+  call ale#linter#Reset()
+
 Execute (Should parse error correctly):
   AssertEqual
   \ [