test(node): add comments about why AxiosError is tested

Author: Zen-cronic

dev-packages/node-integration-tests/package.json

@@ -42,6 +42,7 @@
     "cors": "^2.8.5",
     "cron": "^3.1.6",
     "express": "^4.17.3",
+    "fastify": "^4.23.2",
     "graphql": "^16.3.0",
     "http-terminator": "^3.2.0",
     "ioredis": "^5.4.1",

dev-packages/node-integration-tests/suites/fastify/deprecation/test.ts

@@ -5,6 +5,14 @@ afterAll(() => {
   cleanupChildProcesses();
 });
 
+/**
+ * AxiosError throws before the deprecation warning code is invoked,
+ * so mocking it would have no effect.
+ * 
+ * But the deprecation warning is successfully suppressed.
+ * This can be verified by running the example code as in the original
+ * issue (https://github.com/getsentry/sentry-javascript/issues/12844)
+ */
 test('suppress fastify deprecation warning when `routerPath` property is accessed', async () => {
   // ensures that the assertions in the catch block are called
   expect.assertions(3);