* Toma cada **request** que llega a tu aplicación.
* Puede entonces hacer algo a esa **request** o ejecutar cualquier código necesario.
* Luego pasa la **request** para que sea procesada por el resto de la aplicación (por alguna *path operation*).

        assertEquals(2, set.size());
        Iterator<Entry<String, String>> iterator = set.iterator();
        assertNotNull(iterator);
        assertTrue(iterator.hasNext(), "Expected " + iterator + ".hasNext() to return true");
        assertTrue(iterator.hasNext(), "Expected " + iterator + ".hasNext() to return true");
        Entry<String, String> entry = iterator.next();
        assertNotNull(entry);

  public void testRemovePresentConcurrentWithEntrySetIteration() {
    assertThrows(
        ConcurrentModificationException.class,
        () -> {
          Iterator<Entry<K, V>> iterator = getMap().entrySet().iterator();
          getMap().remove(k0());
          iterator.next();
        });
  }

  @MapFeature.Require({FAILS_FAST_ON_CONCURRENT_MODIFICATION, SUPPORTS_REMOVE})
  @CollectionSize.Require(SEVERAL)

   * bytes long as the original implementation in C++. See http://cl/106539598
   */
  public void testMultipleLengths() {
    int iterations = 800;
    byte[] buf = new byte[iterations * 4];
    int bufLen = 0;
    long h = 0;
    for (int i = 0; i < iterations; ++i) {
      h ^= fingerprint(buf, i);
      h = remix(h);
      buf[bufLen++] = getChar(h);

      h ^= fingerprint(buf, i * i % bufLen);

import com.google.common.collect.testing.features.CollectionFeature;
import java.lang.reflect.Method;
import java.util.Iterator;
import java.util.List;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;
import org.junit.Ignore;

/**
 * Tester to make sure the {@code iterator().remove()} implementation of {@code Multiset} works when
 * there are multiple occurrences of elements.
 *

  @CollectionSize.Require(SEVERAL)
  public void testClearConcurrentWithIteration() {
    assertThrows(
        ConcurrentModificationException.class,
        () -> {
          Iterator<E> iterator = collection.iterator();
          collection.clear();
          iterator.next();
        });
  }

  FilteredMultimapValues(FilteredMultimap<K, V> multimap) {
    this.multimap = checkNotNull(multimap);
  }

  @Override
  public Iterator<V> iterator() {
    return Maps.valueIterator(multimap.entries().iterator());
  }

  @Override
  public boolean contains(@Nullable Object o) {
    return multimap.containsValue(o);
  }

  @Override
  public int size() {

    assertFalse(underlying.containsKey("b"));

    Iterator<String> keyIterator = keys.iterator();
    keyIterator.next();
    keyIterator.remove();
    assertFalse(underlying.containsKey("c"));

    Collection<String> values = map.values();
    values.remove("4");
    assertFalse(underlying.containsKey("d"));

    Iterator<String> valueIterator = values.iterator();
    valueIterator.next();
    valueIterator.remove();

    assertThat(multimap.keySet()).containsExactly("foo", "bar", "cow").inOrder();
    assertThat(multimap.values()).containsExactly(5, 4, 3, 2, 1).inOrder();

    Iterator<Entry<String, Integer>> entryIterator = multimap.entries().iterator();
    assertEquals(immutableEntry("foo", 5), entryIterator.next());
    assertEquals(immutableEntry("bar", 4), entryIterator.next());

Similar a como puedes [agregar `dependencies` a los *path operation decorators*](dependencies-in-path-operation-decorators.md){.internal-link target=_blank}, puedes agregarlos a la aplicación de `FastAPI`.

En ese caso, se aplicarán a todas las *path operations* en la aplicación:

{* ../../docs_src/dependencies/tutorial012_an_py39.py hl[17] *}