issue #587: consistent become_exe() behaviour for older Ansibles.

ansible_mitogen/transport_config.py

@@ -378,7 +378,15 @@ class PlayContextSpec(Spec):
         ]
 
     def become_exe(self):
-        return self._play_context.become_exe
+        # In Ansible 2.8, PlayContext.become_exe always has a default value due
+        # to the new options mechanism. Previously it was only set if a value
+        # ("somewhere") had been specified for the task.
+        # For consistency in the tests, here we make older Ansibles behave like
+        # newer Ansibles.
+        exe = self._play_context.become_exe
+        if exe is None and self._play_context.become_method == 'sudo':
+            exe = 'sudo'
+        return exe
 
     def sudo_args(self):
         return [

tests/ansible/integration/connection_delegation/local_action.yml

@@ -27,7 +27,7 @@
               'remote_name': null,
               'password': null,
               'username': 'root',
-              'sudo_path': null,
+              'sudo_path': 'sudo',
               'sudo_args': ['-H', '-S', '-n'],
             },
             'method': 'sudo',