* ConcurrentHashMap} support for {@code entrySet().add()}</a>.
   */
  @J2ktIncompatible
  @GwtIncompatible // reflection
  public static Method getAddUnsupportedNotPresentMethod() {
    return getMethod(CollectionAddTester.class, "testAdd_unsupportedNotPresent");
  }

Un middleware n'a pas besoin d'être conçu pour FastAPI ou Starlette pour fonctionner, tant qu'il suit la spécification ASGI.

En général, les middlewares ASGI sont des classes qui s'attendent à recevoir une application ASGI en premier argument.

Ainsi, dans la documentation de middlewares ASGI tiers, on vous indiquera probablement de faire quelque chose comme :

```Python

  private static final class OneSizeTestSuiteBuilder<T, E>
      extends FeatureSpecificTestSuiteBuilder<
          OneSizeTestSuiteBuilder<T, E>, OneSizeGenerator<T, E>> {
    @SuppressWarnings("rawtypes") // class literals
    private final List<Class<? extends AbstractTester>> testers;

    @SuppressWarnings("rawtypes") // class literals
    OneSizeTestSuiteBuilder(List<Class<? extends AbstractTester>> testers) {

/** Tests for {@link AbstractFuture} with the cancellation cause system property set */
@AndroidIncompatible // custom classloading

@NullUnmarked
@GwtIncompatible
@J2ktIncompatible
public class AbstractFutureCancellationCauseTest extends TestCase {

  private ClassLoader oldClassLoader;
  private URLClassLoader classReloader;
  private Class<?> settableFutureClass;
  private Class<?> abstractFutureClass;

  @Override

/** Tests for {@link AbstractFuture} with the cancellation cause system property set */
@AndroidIncompatible // custom classloading

@NullUnmarked
@GwtIncompatible
@J2ktIncompatible
public class AbstractFutureCancellationCauseTest extends TestCase {

  private ClassLoader oldClassLoader;
  private URLClassLoader classReloader;
  private Class<?> settableFutureClass;
  private Class<?> abstractFutureClass;

  @Override

app.add_middleware(UnicornMiddleware, some_config="rainbow")
```

`app.add_middleware()` receives a middleware class as the first argument and any additional arguments to be passed to the middleware.

## Integrated middlewares { #integrated-middlewares }

**FastAPI** includes several middlewares for common use cases, we'll see next how to use them.

/// note | Technical Details

// backends (graph/MLIR).
//
// This defines a set of abstract classes that are intended to provide the
// functionality of the opaque C types exposed in the public APIs defined in the
// `c_api_unified_experimental.h` header.
// =============================================================================

// Represents either a MlirTensor or a GraphTensor.
// This base class does not expose any public methods other than to distinguish

        // Test constructor with null message but valid cause
        Exception cause = new IllegalArgumentException("Invalid argument");
        DictionaryException exception = new DictionaryException(null, cause);

        assertNotNull(exception);
        assertNull(exception.getMessage());
        assertNotNull(exception.getCause());
        assertEquals(cause, exception.getCause());
    }

    @Test

Un middleware no tiene que estar hecho para FastAPI o Starlette para funcionar, siempre que siga la especificación ASGI.

En general, los middlewares ASGI son clases que esperan recibir una aplicación ASGI como primer argumento.

Entonces, en la documentación de middlewares ASGI de terceros probablemente te indicarán que hagas algo como:

```Python
from unicorn import UnicornMiddleware

  static class CustomRuntimeException extends RuntimeException {}

  public void testCatching() throws Exception {
    FluentFuture<?> f =
        FluentFuture.from(immediateFailedFuture(new CustomRuntimeException()))
            .catching(Throwable.class, Object::getClass, directExecutor());
    assertThat(f.get()).isEqualTo(CustomRuntimeException.class);
  }