Add Mock.assert_called()

Issue #26323: Add assert_called() and assert_called_once() methods to
unittest.mock.Mock.
diff --git a/NEWS b/NEWS
index 2e13b8a..2120418 100644
--- a/NEWS
+++ b/NEWS
@@ -1,6 +1,9 @@
 Library
 -------
 
+- Issue #26323: Add Mock.assert_called() and Mock.assert_called_once()
+  methods to unittest.mock. Patch written by Amit Saha.
+
 - Issue #22138: Fix mock.patch behavior when patching descriptors. Restore
   original values after patching. Patch contributed by Sean McCully.