node-mocks-http VS testing-nestjs

It is possible to test by calling the app or individual middleware directly, but that's done by using request/response mocks (for example, using node-mocks-http) and probably doesn't save much overhead when testing locally.

Yes, but when every function handler is separate from the router, then you can use node-mocks-http to test each handler, to test the router is simpler to use supertest to write integration tests, for E2E tests I personally recommend [pactum](pactumjs.github.io/)

It depends of how you mock the request and response that you passed to ExecutionContext because the response should be modified. I recommend you to use node-mocks-http

To echo the other's here, Nx has been an amazing dev experience for me! I use it for ogma, for nest-commander, testing-nestjs, and for nest-samples and @nest-lab/, all using pnpm as a package manager.

The prisma sample app in the testing-nestjs repository does a great job on showing how to do testing a NestJS app with Prisma.

Example https://github.com/jmcdo29/testing-nestjs/blob/8519ae7043d1dde5ae12a5d8f8ab02ea3c3c2fcf/apps/complex-sample/src/cat/cat.interceptor.spec.ts

Question: for your e2e tests will you be using something like supertestto send the gql request? And if so, could I suggest you look at pactum which (in my opinion) has a stronger API and better gql support. I've got an example here if you need it

Test files usually shouldn't be too large. You should just need a simple mock for each injected dependency for the service. You can see a lot of examples I have here. If you could show your test file it may help us figure out why it might be really large.

Then there's also a @nestjs/testing package that can be used for overriding these injections during tests to make for super easy unit testing (in my opinion) and a large repo of examples here.