The official documentation (and the templated starter) for Nest.js
shows an end-to-end test that uses the Test.createTestModule() helper to
create an instance of INestApplication that is used for the subsequent tests.
It may simply be an issue of nomenclature -- when I see the phrase "end-to-end", this makes me think the intention is that of an integration test, where all components of the application are integrated and then exercised together in a testing context.
To be fair to Nest, the documentation states that this is not quite an integration test:
... closer to the kind of interaction that end-users will have with the production system ...
The key word here is closer -- these tests in Nest approximate the type of
behavior a consumer app might see, but it's not the full story. As a basic
example, adding a ValidationPipe to the global pipes that validates all
incoming request bodies against their configured DTOs will not be triggered when
using the Test.createTestModule() approach.
This difference is demonstrated in
test/app.e2e-spec.ts:
AppController (e2e)
using testing module fixture
POST / with an empty body
✓ returns a successful empty response (607ms)
using bootstrapped app
POST / with an empty body
✓ returns a 400 error (29ms)
It's not clear what value a "Nest-style" e2e test provides by not being a full integration test, so there are a couple options:
-
Stop using
Test.createTestModule()in all e2e tests entirely and instead use the actual app instance that is run in development and all other environments -
Abandon the use of e2e tests as a label and instead move to (potentially) more appropriately named "integration" tests (e.g.
app.integration.spec.ts)