Add test for consolidating grouped field sets properly into deferred fragments (#3997)

Group field sets should be properly consolidated when some of the fields
in a sibling defer overlap with a child deferred fragment.

The child deferred fragment should not prompt creation of an additional incremental data record for that field, because the field would always be sent with the parent.

Author: yaacovCR

src/execution/__tests__/defer-test.ts

@@ -1138,6 +1138,61 @@ describe('Execute: defer directive', () => {
     ]);
   });
 
+  it('Correctly bundles varying subfields into incremental data records unique by defer combination, ignoring fields in a fragment masked by a parent defer', async () => {
+    const document = parse(`
+      query HeroNameQuery {
+        ... @defer {
+          hero {
+            id
+          }
+        }
+        ... @defer {
+          hero {
+            name
+            shouldBeWithNameDespiteAdditionalDefer: name
+            ... @defer {
+              shouldBeWithNameDespiteAdditionalDefer: name
+            }
+          }
+        }
+      }
+    `);
+    const result = await complete(document);
+    expectJSON(result).toDeepEqual([
+      {
+        data: {},
+        pending: [
+          { id: '0', path: [] },
+          { id: '1', path: [] },
+        ],
+        hasNext: true,
+      },
+      {
+        incremental: [
+          {
+            data: { hero: {} },
+            id: '0',
+          },
+          {
+            data: { id: '1' },
+            id: '0',
+            subPath: ['hero'],
+          },
+          {
+            data: {
+              name: 'Luke',
+              shouldBeWithNameDespiteAdditionalDefer: 'Luke',
+            },
+            id: '1',
+            subPath: ['hero'],
+          },
+        ],
+        completed: [{ id: '0' }, { id: '1' }],
+        hasNext: false,
+      },
+    ]);
+  });
+
   it('Nulls cross defer boundaries, null first', async () => {
     const document = parse(`
       query {