Tweak to only show msg on assert failure if set

lib/ansible/runner/action_plugins/assert.py

@@ -38,8 +38,7 @@ class ActionModule(object):
             args.update(complex_args)
         args.update(utils.parse_kv(module_args))
 
-        msg = 'assertion failed'
-
+        msg = None
         if 'msg' in args:
             msg = args['msg']
 
@@ -50,8 +49,16 @@ class ActionModule(object):
             args['that'] = [ args['that'] ]
 
         for that in args['that']:
-            result = utils.check_conditional(that, self.runner.basedir, inject, fail_on_undefined=True)
-            if not result:
-                return ReturnData(conn=conn, result=dict(failed=True, msg=msg, assertion=that, evaluated_to=result))
+            test_result = utils.check_conditional(that, self.runner.basedir, inject, fail_on_undefined=True)
+            if not test_result:
+                result = dict(
+                   failed       = True,
+                   evaluated_to = test_result,
+                   assertion    = that,
+                )
+                if msg:
+                    result['msg'] = msg
+                return ReturnData(conn=conn, result=result)
 
         return ReturnData(conn=conn, result=dict(msg='all assertions passed'))
+