They tend to require more complex configurations, a message/job queue manager, like RabbitMQ or Redis, but they allow you to run background tasks in multiple processes, and especially, in multiple servers.

* 📝 Update includes for `docs/en/docs/tutorial/body-updates.md`. PR [#12712](https://github.com/fastapi/fastapi/pull/12712) by [@davioc](https://github.com/davioc).
* 📝 Remove mention of Celery in the project generators. PR [#12742](https://github.com/fastapi/fastapi/pull/12742) by [@david-caro](https://github.com/david-caro).

        final ConstraintValidatorContext context = null;

        // Test basic patterns that should be valid
        String[] potentiallyValidCrons = { "0 0 * * * ?", // Every hour
                "0 */15 * * * ?", // Every 15 minutes
                "0 0 12 * * ?", // Daily at noon
                "0 15 10 ? * MON-FRI" // Weekdays at 10:15
        };

        // Test each pattern and see what actually works

# Middleware { #middleware }

You can add middleware to **FastAPI** applications.

A "middleware" is a function that works with every **request** before it is processed by any specific *path operation*. And also with every **response** before returning it.

* It takes each **request** that comes to your application.
* It can then do something to that **request** or run any needed code.

    return Collections.unmodifiableList(asStripes);
  }

  // Static factories

  /**
   * Creates a {@code Striped<L>} with eagerly initialized, strongly referenced locks. Every lock is
   * obtained from the passed supplier.
   *
   * @param stripes the minimum number of stripes (locks) required
   * @param supplier a {@code Supplier<L>} object to obtain locks from

 *
 * @author Charles Fry
 */
@NullUnmarked
public final class TestingWeighers {

  /** Returns a {@link Weigher} that returns the given {@code constant} for every request. */
  static Weigher<Object, Object> constantWeigher(int constant) {
    return new ConstantWeigher(constant);
  }

  /** Returns a {@link Weigher} that uses the integer key as the weight. */

Then wrap the WSGI (e.g. Flask) app with the middleware.

And then mount that under a path.

{* ../../docs_src/wsgi/tutorial001.py hl[2:3,3] *}

## Check it { #check-it }

Now, every request under the path `/v1/` will be handled by the Flask application.

And the rest will be handled by **FastAPI**.

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.

    // launched by this test is either:
    //
    // (a) Blocked attempting to enter the monitor.
    // (b) Waiting for the single guard to become satisfied.
    // (c) Occupying the monitor and awaiting the tearDownLatch.
    //
    // Except for (c), every thread should occupy the monitor very briefly, and every thread leaves

 * Mockito to guarantee that implementation classes do not inadvertently
 * bypass the filter logic.
 */
public class SmbFileFilterTest {

    /**
     * A minimal implementation that accepts every {@link SmbFile}.
     */
    private final SmbFileFilter ALWAYSACTIVE = new SmbFileFilter() {
        @Override
        public boolean accept(SmbFile file) throws SmbException {