Reference implementation of defer and stream spec (#4537)

Author: yaacovCR

src/execution/__tests__/cancellation-test.ts

@@ -42,6 +42,52 @@ function collectRootFields(query: string) {
 
 describe('collectFields', () => {
   describe('overlapping fragment spreads', () => {
+    it('should not collect a deferred spread after a non-deferred spread has been collected', () => {
+      const { newDeferUsages } = collectRootFields(`
+        query {
+          ...FragmentName
+          ...FragmentName @defer
+        }
+        fragment FragmentName on Query {
+          field
+        }
+      `);
+
+      expect(newDeferUsages).to.have.lengthOf(0);
+    });
+
+    it('should not collect a deferred spread after a deferred spread has been collected', () => {
+      const { newDeferUsages } = collectRootFields(`
+        query {
+          ...FragmentName @defer
+          ...FragmentName @defer
+        }
+        fragment FragmentName on Query {
+          field
+        }
+      `);
+
+      expect(newDeferUsages).to.have.lengthOf(1);
+    });
+
+    it('should collect a non-deferred spread after a deferred spread has been collected', () => {
+      const { groupedFieldSet } = collectRootFields(`
+        query {
+          ...FragmentName @defer
+          ...FragmentName
+        }
+        fragment FragmentName on Query {
+          field
+        }
+      `);
+
+      const fieldDetailsList = groupedFieldSet.get('field');
+
+      invariant(fieldDetailsList != null);
+
+      expect(fieldDetailsList).to.have.lengthOf(2);
+    });
+
     it('should not collect a non-deferred spread after a non-deferred spread has been collected', () => {
       const { groupedFieldSet } = collectRootFields(`
         query {