[fix] Skip connection check when firmware image unchanged

Author: Eeshu-Yadav

openwisp_firmware_upgrader/base/models.py

@@ -409,7 +409,7 @@ def clean(self):
                     )
                 }
             )
-        if self.device.deviceconnection_set.count() < 1:
+        if self.image_has_changed and self.device.deviceconnection_set.count() < 1:
             raise ValidationError(
                 _(
                     "This device does not have a related connection object defined "

openwisp_firmware_upgrader/tests/test_models.py

@@ -177,14 +177,11 @@ def test_device_fw_no_connection(self):
         else:
             self.fail("ValidationError not raised")
 
-    def test_device_fw_credentials_removed_after_assignment(self):
+    def test_device_fw_save_after_credentials_removed(self):
         """Regression test for #250."""
         device_fw = self._create_device_firmware()
-        device_fw.upgrade_options = {"n": True}
         device_fw.device.deviceconnection_set.all().delete()
-        with self.assertRaises(ValidationError) as ctx:
-            device_fw.full_clean()
-        self.assertIn("connection", str(ctx.exception).lower())
+        device_fw.full_clean()
 
     def test_invalid_board(self):
         image = FIRMWARE_IMAGE_MAP[self.TPLINK_4300_IMAGE]