add tests for memoization of collectSubfields

extracted from #4548

Author: yaacovCR

src/execution/Executor.ts

@@ -64,7 +64,7 @@ import { getArgumentValues } from './values.js';
  * type. Memoizing ensures the subfields are not repeatedly calculated, which
  * saves overhead when resolving lists of values.
  */
-const collectSubfields = memoize3(
+export const collectSubfields = memoize3(
   (
     validatedExecutionArgs: ValidatedExecutionArgs,
     returnType: GraphQLObjectType,

src/execution/__tests__/executor-test.ts

@@ -7,6 +7,7 @@ import { resolveOnNextTick } from '../../__testUtils__/resolveOnNextTick.js';
 import { inspect } from '../../jsutils/inspect.js';
 import { promiseWithResolvers } from '../../jsutils/promiseWithResolvers.js';
 
+import type { FieldNode } from '../../language/ast.js';
 import { Kind } from '../../language/kinds.js';
 import { parse } from '../../language/parser.js';
 
@@ -27,7 +28,9 @@ import {
 } from '../../type/scalars.js';
 import { GraphQLSchema } from '../../type/schema.js';
 
-import { execute, executeSync } from '../execute.js';
+import type { FieldDetailsList } from '../collectFields.js';
+import { execute, executeSync, validateExecutionArgs } from '../execute.js';
+import { collectSubfields } from '../Executor.js';
 
 describe('Execute: Handles basic execution tasks', () => {
   it('executes arbitrary code', async () => {
@@ -1412,4 +1415,53 @@ describe('Execute: Handles basic execution tasks', () => {
       ],
     });
   });
+
+  it('memoizes collectSubfields results', () => {
+    const deepType = new GraphQLObjectType({
+      name: 'DeepType',
+      fields: {
+        name: { type: GraphQLString },
+      },
+    });
+    const schema = new GraphQLSchema({
+      query: new GraphQLObjectType({
+        name: 'Query',
+        fields: {
+          deep: { type: deepType },
+        },
+      }),
+    });
+    const document = parse('{ deep { name } }');
+    const validatedExecutionArgs = validateExecutionArgs({
+      schema,
+      document,
+    });
+
+    assert('schema' in validatedExecutionArgs);
+
+    const operation = validatedExecutionArgs.operation;
+    const node = operation.selectionSet.selections[0] as FieldNode;
+
+    const fieldDetailsList: FieldDetailsList = [{ node }];
+
+    const first = collectSubfields(
+      validatedExecutionArgs,
+      deepType,
+      fieldDetailsList,
+    );
+
+    const second = collectSubfields(
+      validatedExecutionArgs,
+      deepType,
+      fieldDetailsList,
+    );
+
+    expect(second).to.equal(first);
+
+    const third = collectSubfields(validatedExecutionArgs, deepType, [
+      { node },
+    ]);
+
+    expect(third).to.not.equal(first);
+  });
 });