add the ability to make a layer readonly

test/property/test_property_readonly.py

@@ -0,0 +1,15 @@
+from unittest import TestCase
+from owrx.property import PropertyLayer, PropertyReadOnly, PropertyWriteError
+
+
+class PropertyReadOnlyTest(TestCase):
+    def testPreventsWrites(self):
+        layer = PropertyLayer()
+        layer["testkey"] = "initial value"
+        ro = PropertyReadOnly(layer)
+        with self.assertRaises(PropertyWriteError):
+            ro["testkey"] = "new value"
+        with self.assertRaises(PropertyWriteError):
+            ro["otherkey"] = "testvalue"
+        self.assertEqual(ro["testkey"], "initial value")
+        self.assertNotIn("otherkey", ro)