Additional differ test: flattening differ should not produce DELETE and CREATE mutation for the same tag in the same frame

Summary:
See additional assertion. Tests still pass, so no other change was necessary.

Changelog: [Internal]

Differential Revision: D23775553

fbshipit-source-id: 57d3191f25dd55ab4da189207f6d201a31b175e0

ReactCommon/react/renderer/mounting/tests/ShadowTreeLifeCycleTest.cpp

@@ -5,11 +5,14 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#include <vector>
+
 #include <glog/logging.h>
 #include <gtest/gtest.h>
 
 #include <react/renderer/components/root/RootComponentDescriptor.h>
 #include <react/renderer/components/view/ViewComponentDescriptor.h>
+#include <react/renderer/mounting/ShadowViewMutation.h>
 #include <react/renderer/mounting/Differentiator.h>
 #include <react/renderer/mounting/stubs.h>
 
@@ -102,6 +105,25 @@ static void testShadowNodeTreeLifeCycle(
       auto mutations = calculateShadowViewMutations(
           *currentRootNode, *nextRootNode, useFlattener);
 
+      // If using flattener: make sure that in a single frame, a DELETE for a view is not
+      // followed by a CREATE for the same view.
+      if (useFlattener) {
+        std::vector<int> deletedTags{};
+        for (auto const& mutation : mutations) {
+          if (mutation.type == ShadowViewMutation::Type::Delete) {
+            deletedTags.push_back(mutation.oldChildShadowView.tag);
+          }
+        }
+        for (auto const& mutation : mutations) {
+          if (mutation.type == ShadowViewMutation::Type::Create) {
+            if (std::find(deletedTags.begin(), deletedTags.end(), mutation.newChildShadowView.tag) != deletedTags.end()) {
+              LOG(ERROR) << "Deleted tag was recreated in mutations list: [" << mutation.newChildShadowView.tag << "]";
+              FAIL();
+            }
+          }
+        }
+      }
+
       // Mutating the view tree.
       viewTree.mutate(mutations);