lib: test for fetch mock without prior invocation

The purpose of this test is to verify the correct behavior of stubbing
the globalThis.fetch method with custom implementation. It checks
whether the stubbed fetch function correctly returns the expected
response without calling fetch iteself first.

test/parallel/test-fetch-mock.js

@@ -0,0 +1,19 @@
+'use strict';
+require('../common');
+const { mock, test } = require('node:test');
+const assert = require('node:assert');
+
+test('should correctly stub globalThis.fetch', async () => {
+  const customFetch = async (url) => {
+    return {
+      text: async () => 'foo',
+    };
+  };
+
+  mock.method(globalThis, 'fetch', customFetch);
+
+  const response = await globalThis.fetch('some-url');
+  const text = await response.text();
+
+  assert.strictEqual(text, 'foo');
+});