Fix anchor

Author: Benbb96

src/content/4/en/part4b.md

@@ -1057,7 +1057,7 @@ and by extending the Jest definitions in the <i>package.json</i> as follows
 
 Write a test that verifies that the unique identifier property of the blog posts is named <i>id</i>, by default the database names the property <i>_id</i>. Verifying the existence of a property is easily done with Jest's [toBeDefined](https://jestjs.io/docs/en/expect#tobedefined) matcher.
 
-Make the required changes to the code so that it passes the test. The [toJSON](/en/part3/saving_data_to_mongo_db#backend-connected-to-a-database) method discussed in part 3 is an appropriate place for defining the <i>id</i> parameter.
+Make the required changes to the code so that it passes the test. The [toJSON](/en/part3/saving_data_to_mongo_db#connecting-the-backend-to-a-database) method discussed in part 3 is an appropriate place for defining the <i>id</i> parameter.
 
 #### 4.10: Blog list tests, step3