Cover basic GCC functionality with tests

autoload/ale/engine.vim

@@ -95,6 +95,12 @@ function! s:KillHandler(timer) abort
 endfunction
 
 function! ale#engine#ClearJob(job) abort
+    if get(g:, 'ale_run_synchronously') == 1
+        call remove(s:job_info_map, a:job)
+
+        return
+    endif
+
     let l:job_id = s:GetJobID(a:job)
 
     if has('nvim')
@@ -515,7 +521,26 @@ function! s:RunJob(options) abort
         let l:read_buffer = 0
     endif
 
-    if has('nvim')
+    if !has('nvim')
+        " The command will be executed in a subshell. This fixes a number of
+        " issues, including reading the PATH variables correctly, %PATHEXT%
+        " expansion on Windows, etc.
+        "
+        " NeoVim handles this issue automatically if the command is a String.
+        let l:command = has('win32')
+        \   ?  'cmd /c ' . l:command
+        \   : split(&shell) + split(&shellcmdflag) + [l:command]
+    endif
+
+    if get(g:, 'ale_run_synchronously') == 1
+        " Find a unique Job value to use, which will be the same as the ID for
+        " running commands synchronously. This is only for test code.
+        let l:job = len(s:job_info_map) + 1
+
+        while has_key(s:job_info_map, l:job)
+            let l:job += 1
+        endwhile
+    elseif has('nvim')
         if l:output_stream ==# 'stderr'
             " Read from stderr instead of stdout.
             let l:job = jobstart(l:command, {
@@ -559,15 +584,6 @@ function! s:RunJob(options) abort
             let l:job_options.out_cb = function('s:GatherOutputVim')
         endif
 
-        " The command will be executed in a subshell. This fixes a number of
-        " issues, including reading the PATH variables correctly, %PATHEXT%
-        " expansion on Windows, etc.
-        "
-        " NeoVim handles this issue automatically if the command is a String.
-        let l:command = has('win32')
-        \   ?  'cmd /c ' . l:command
-        \   : split(&shell) + split(&shellcmdflag) + [l:command]
-
         " Vim 8 will read the stdin from the file's buffer.
         let l:job = job_start(l:command, l:job_options)
     endif
@@ -576,7 +592,9 @@ function! s:RunJob(options) abort
     let l:job_id = 0
 
     " Only proceed if the job is being run.
-    if has('nvim') || (l:job !=# 'no process' && job_status(l:job) ==# 'run')
+    if has('nvim')
+    \ || get(g:, 'ale_run_synchronously') == 1
+    \ || (l:job !=# 'no process' && job_status(l:job) ==# 'run')
         " Add the job to the list of jobs, so we can track them.
         call add(g:ale_buffer_info[l:buffer].job_list, l:job)
 
@@ -596,6 +614,16 @@ function! s:RunJob(options) abort
     else
         let g:ale_buffer_info[l:buffer].history = []
     endif
+
+    if get(g:, 'ale_run_synchronously') == 1
+        " Run a command synchronously if this test option is set.
+        let s:job_info_map[l:job_id].output = systemlist(
+        \   type(l:command) == type([])
+        \   ?  join(l:command[0:1]) . ' ' . shellescape(l:command[2])
+        \   : l:command
+        \)
+        call s:HandleExit(l:job)
+    endif
 endfunction
 
 " Determine which commands to run for a link in a command chain, or