Ensure NmtBase.state always returns a string (#506)

Fixes #500

Author: erlend-aasland

canopen/nmt.py

@@ -86,10 +86,10 @@ def state(self) -> str:
         - 'RESET'
         - 'RESET COMMUNICATION'
         """
-        if self._state in NMT_STATES:
+        try:
             return NMT_STATES[self._state]
-        else:
-            return self._state
+        except KeyError:
+            return f"UNKNOWN STATE '{self._state}'"
 
     @state.setter
     def state(self, new_state: str):

test/test_nmt.py

@@ -88,12 +88,11 @@ def test_nmt_master_on_heartbeat_initialising(self):
         state = self.node.nmt.wait_for_heartbeat(self.TIMEOUT)
         self.assertEqual(state, "PRE-OPERATIONAL")
 
-    @unittest.expectedFailure
     def test_nmt_master_on_heartbeat_unknown_state(self):
         task = self.net.send_periodic(self.COB_ID, [0xcb], self.PERIOD)
         self.addCleanup(task.stop)
         state = self.node.nmt.wait_for_heartbeat(self.TIMEOUT)
-        # Expect the high bit to be masked out, and and unknown state string to
+        # Expect the high bit to be masked out, and a formatted string to
         # be returned.
         self.assertEqual(state, "UNKNOWN STATE '75'")