fix test file writing

Author: BenLubar

test/main.lua

@@ -1,12 +1,6 @@
 local args = {...}
 local done_command = args[1]
 
-function set_test_stage(stage)
-    local f = io.open('test_stage.txt', 'w')
-    f:write(stage)
-    f:close()
-end
-
 print('Running tests')
 
 local status = dfhack.run_command('ai', 'validate')
@@ -16,7 +10,9 @@ else
     dfhack.printerr('test errored: df-ai:validate: status=' .. tostring(status))
 end
 
-set_test_stage('done')
+local f = io.open('test_status.json', 'w')
+f:write('{"ai":"passed"}')
+f:close()
 if done_command then
     dfhack.run_command(done_command)
 end