Procedurally generated tests with an async dependency

[calebmer]

I have a project which will automatically generate an API based on some schema data which must be fetched asynchronously. I’d like to provide a testing interface for these automatically generated APIs, say the function testApi(api) which will run the necessary describes and its to create an entire test suite for that api. So here’s an example:

// `testApi` is being called in the global file scope,
// `await` is just demonstrating what I want to do here.
testApi(await generateApi())

function testApi (api) {
  describe(api.name, () => {
    api.getRoutes().forEach(route => {
      describe(route.path, () => {
        it('works', () => {
          expect(true).toBe(true)
        })
      })
    })
  })
}

My first idea was to do something like this:

let api

beforeAll(async () => {
  api = await generateApi()
})

describe('my API tests', () => {
  testApi(api)
})

However, there are two incorrect assumptions here, first is that Jest supports beforeAll (as far as I know) and that describe is executed lazily (i.e. after beforeAll resolves). Any ideas?

This is most definitely a niche use case, but I’d like to hear if there is a solution and/or interest to support this use case.

[cpojer]

In Jasmine you need to define all your tests (calls to it or describe) before the end of the test. This is a limitation we can't do so much about right now. Can you make it so your tests are generated synchronously? beforeAll definitely does work in Jest, however and can be made async too. beforeAll is called before the first call to it.

[aaronabramov]

if your definition is fetched asynchronously there is nothing we can really do to make it work :(
i think the best solution would be to stick it all into one test case and provide nice messages if something failed:

test('some api', () => {
  generateApi().then(api => {
    return promiseAll(api.routes.map(route => {
      return new Promise(route => invariant(true, `${api.name} ${route.name} test failed because of something`));
    });
  });
});

[calebmer]

Yeah, probably the direction I’ll go. Although I have been witnessing a Twitter firestorm recently on top level awaits lol, maybe one day that can be a solution 🙃

(lot’s of sarcasm, please don’t take seriously)

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