Document default configuration breaking change

add unit test

Author: roycaihw

CHANGELOG.md

@@ -24,6 +24,9 @@ Kubernetes API Version: 1.16.14
 
 Kubernetes API Version: 1.16.14
 
+**Breaking Change:**
+- `kubernetes.config.Configuration()` no longer returns the default configuration. Use `kubernetes.config.Configuration.get_default_copy()` now to get the default configuration. [OpenAPITools/openapi-generator#4485](https://github.com/OpenAPITools/openapi-generator/pull/4485), [OpenAPITools/openapi-generator#5315](https://github.com/OpenAPITools/openapi-generator/pull/5315)
+
 **API Change:**
 
 - Resolve regression in metadata.managedFields handling in update/patch requests submitted by older API clients ([#91748](https://github.com/kubernetes/kubernetes/pull/91748), [@apelisse](https://github.com/apelisse)) [SIG API Machinery and Testing]

kubernetes/test/test_configuration.py

@@ -0,0 +1,39 @@
+# coding: utf-8
+
+import unittest
+
+from kubernetes.client import Configuration
+
+class TestConfiguration(unittest.TestCase):
+
+    def setUp(self):
+        pass
+
+    def tearDown(self):
+        # reset Configuration
+        Configuration.set_default(None)
+
+    def testConfiguration(self):
+        # check that different instances use different dictionaries
+        c1 = Configuration()
+        c2 = Configuration()
+        self.assertNotEqual(id(c1.api_key), id(c2.api_key))
+        self.assertNotEqual(id(c1.api_key_prefix), id(c2.api_key_prefix))
+
+    def testDefaultConfiguration(self):
+        # prepare default configuration
+        c1 = Configuration(host="example.com")
+        c1.debug = True
+        Configuration.set_default(c1)
+
+        # get default configuration
+        c2 = Configuration.get_default_copy()
+        self.assertEqual(c2.host, "example.com")
+        self.assertTrue(c2.debug)
+
+        self.assertNotEqual(id(c1.api_key), id(c2.api_key))
+        self.assertNotEqual(id(c1.api_key_prefix), id(c2.api_key_prefix))
+
+
+if __name__ == '__main__':
+    unittest.main()