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* Updated .py files with Optional tag (up to body_nested_models) * Update optionals * docs_src/ all updates, few I was unsure of * Updated markdown files with Optional param * es: Add Optional typing to index.md * Last of markdown files updated with Optional param * Update highlight lines * it: Add Optional typings * README.md: Update with Optional typings * Update more highlight increments * Update highlights * schema-extra-example.md: Update highlights * updating highlighting on website to reflect .py changes * Update highlighting for query-params & response-directly * Address PR comments * Get rid of unnecessary comment * ⏪ Revert Optional in Chinese docs as it probably also requires changes in text * 🎨 Apply format * ⏪ Revert modified example * ♻️ Simplify example in docs * 📝 Update OpenAPI callback example to use Optional * ✨ Add Optional types to tests * 📝 Update docs about query params, default to using Optional * 🎨 Update code examples line highlighting * 📝 Update nested models docs to use "type parameters" instead of "subtypes" * 📝 Add notes about FastAPI usage of None including: = None and = Query(None) and clarify relationship with Optional[str] * 📝 Add note about response_model_by_alias * ♻️ Simplify query param list example * 🔥 Remove test for removed example * ✅ Update test for updated example Co-authored-by: Christopher Nguyen <chrisngyn99@gmail.com> Co-authored-by: yk396 <yk396@cornell.edu> Co-authored-by: Kai Chen <kaichen120@gmail.com>
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Testing Dependencies with Overrides
Overriding dependencies during testing
There are some scenarios where you might want to override a dependency during testing.
You don't want the original dependency to run (nor any of the sub-dependencies it might have).
Instead, you want to provide a different dependency that will be used only during tests (possibly only some specific tests), and will provide a value that can be used where the value of the original dependency was used.
Use cases: external service
An example could be that you have an external authentication provider that you need to call.
You send it a token and it returns an authenticated user.
This provider might be charging you per request, and calling it might take some extra time than if you had a fixed mock user for tests.
You probably want to test the external provider once, but not necessarily call it for every test that runs.
In this case, you can override the dependency that calls that provider, and use a custom dependency that returns a mock user, only for your tests.
Use the app.dependency_overrides attribute
For these cases, your FastAPI application has an attribute app.dependency_overrides, it is a simple dict.
To override a dependency for testing, you put as a key the original dependency (a function), and as the value, your dependency override (another function).
And then FastAPI will call that override instead of the original dependency.
{!../../../docs_src/dependency_testing/tutorial001.py!}
!!! tip You can set a dependency override for a dependency used anywhere in your FastAPI application.
The original dependency could be used in a *path operation function*, a *path operation decorator* (when you don't use the return value), a `.include_router()` call, etc.
FastAPI will still be able to override it.
Then you can reset your overrides (remove them) by setting app.dependency_overrides to be an empty dict:
app.dependency_overrides = {}
!!! tip If you want to override a dependency only during some tests, you can set the override at the beginning of the test (inside the test function) and reset it at the end (at the end of the test function).