* Since it's an interface with only static final fields, there is no complex logic to test.
     */
    @Test
    void testConstants() {
        // A simple assertion to verify that some of the constants have the expected values.
        // This confirms that the class is on the classpath and its fields are accessible.

///

It will:

* Return that status code in the response.
* Document it as such in the OpenAPI schema (and so, in the user interfaces):

<img src="/img/tutorial/response-status-code/image01.png">

/// note

Some response codes (see the next section) indicate that the response does not have a body.

FastAPI knows this, and will produce OpenAPI docs that state there is no response body.

///

        // 4 (dataCount) + 4 (dataOffset) + 1 (setupCount) + 2 (function)
        assertEquals(38, bytesWritten, "Number of bytes written should be 38 for primary transaction");

        // Verify some key values
        assertEquals(smbComNtTransaction.maxSetupCount, dst[0], "maxSetupCount should be written correctly");
        assertEquals(smbComNtTransaction.totalParameterCount, SmbComTransaction.readInt4(dst, 3),

# Custom Request and APIRoute class { #custom-request-and-apiroute-class }

In some cases, you may want to override the logic used by the `Request` and `APIRoute` classes.

In particular, this may be a good alternative to logic in a middleware.

For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.

### Load Balancer { #load-balancer }

When using containers, you would normally have some component **listening on the main port**. It could possibly be another container that is also a **TLS Termination Proxy** to handle **HTTPS** or some similar tool.

Then your API will (let's imagine):

* Send the invoice to some customer of the external developer.
* Collect the money.
* Send a notification back to the API user (the external developer).
    * This will be done by sending a POST request (from *your API*) to some *external API* provided by that external developer (this is the "callback").

    assertThat(notifications).hasSize(1);
    CacheTesting.checkEmpty(cache);
  }

  public void testUpdates() {
    cache.put(key, "1");
    // simultaneous update for same key, some null, some non-null
    doParallelCacheOp(
        count,
        n -> {
          cache.asMap().compute(key, (k, v) -> n % 2 == 0 ? v + delimiter + n : null);
        });
    assertThat(cache.size()).isAtMost(1);
  }

  // TODO(b/192446998): Remove this override after tools understand nullness better.
  public @Nullable V put(K key, @ParametricNullness V value) {
    return super.put(key, value);
  }

  @CanIgnoreReturnValue
  @Override
  @SuppressWarnings("RedundantOverride") // b/192446478: RedundantOverride ignores some annotations.

# Global Dependencies { #global-dependencies }

For some types of applications you might want to add dependencies to the whole application.

Similar to the way you can [add `dependencies` to the *path operation decorators*](dependencies-in-path-operation-decorators.md){.internal-link target=_blank}, you can add them to the `FastAPI` application.

In that case, they will be applied to all the *path operations* in the application:

Vous pouvez utiliser <a href="https://www.docker.com/" class="external-link" target="_blank">**Docker**</a> pour le déploiement. Il présente plusieurs avantages comme la sécurité, la réplicabilité, la simplicité de développement, etc.

Si vous utilisez Docker, vous pouvez utiliser l'image Docker officielle :