Improve test

packages/executors/http/tests/buildHTTPExecutor.test.ts

@@ -1,6 +1,6 @@
 import { createServer, Server } from 'http';
 import { GraphQLError, parse } from 'graphql';
-import { createGraphQLError, ExecutionResult } from '@graphql-tools/utils';
+import { createGraphQLError, ExecutionResult, isAsyncIterable } from '@graphql-tools/utils';
 import { ReadableStream, Request, Response } from '@whatwg-node/fetch';
 import { assertAsyncIterable } from '../../../loaders/url/tests/test-utils.js';
 import { buildHTTPExecutor } from '../src/index.js';
@@ -259,19 +259,21 @@ describe('buildHTTPExecutor', () => {
     const executor = buildHTTPExecutor({
       useGETForQueries: true,
       fetch() {
-        return new Response(JSON.stringify({ errors: [{ message: 'test error' }] }), {
-          headers: { 'Content-Type': 'application/json' },
-        });
+        return Response.json({ errors: [{ message: 'test error' }] });
       },
     });
 
-    const result = (await executor({
+    const result = await executor({
       document: parse(/* GraphQL */ `
         query {
           hello
         }
       `),
-    })) as ExecutionResult;
+    });
+
+    if (isAsyncIterable(result)) {
+      throw new Error('Expected result to be an ExecutionResult');
+    }
 
     expect(result.errors?.[0]).toBeInstanceOf(GraphQLError);
     expect(result.errors?.[0]?.extensions).toMatchObject({