Merge pull request #3240 from ultimecia7/docfix

Fix testing documentation to demonstrate using test client with teardown

docs/testing.rst

@@ -54,12 +54,11 @@ the application for testing and initializes a new database::
     def client():
         db_fd, flaskr.app.config['DATABASE'] = tempfile.mkstemp()
         flaskr.app.config['TESTING'] = True
-        client = flaskr.app.test_client()
-
-        with flaskr.app.app_context():
-            flaskr.init_db()
-
-        yield client
+        
+        with flaskr.app.test_client() as client:
+            with flaskr.app.app_context():
+                flaskr.init_db()
+            yield client
 
         os.close(db_fd)
         os.unlink(flaskr.app.config['DATABASE'])