En este caso, podrías querer documentar cómo esa API externa *debería* verse. Qué *path operation* debería tener, qué cuerpo debería esperar, qué response debería devolver, etc.

## Una aplicación con callbacks

Veamos todo esto con un ejemplo.

Imagina que desarrollas una aplicación que permite crear facturas.

Estas facturas tendrán un `id`, `title` (opcional), `customer`, y `total`.

 * @author Louis Wasserman
 * @since 2.0
 */
@GwtCompatible
public abstract class ForwardingMap<K extends @Nullable Object, V extends @Nullable Object>
    extends ForwardingObject implements Map<K, V> {
  // TODO(lowasser): identify places where thread safety is actually lost

  /** Constructor for use by subclasses. */
  protected ForwardingMap() {}

  @Override
  protected abstract Map<K, V> delegate();

  @Override

      }
      return false;
    }

    @Override
    public int hashCode() {
      return f.hashCode() ^ p.hashCode();
    }

    @Override
    public String toString() {
      // TODO(cpovirk): maybe make this look like the method call does ("Predicates.compose(...)")
      return p + "(" + f + ")";
    }

    @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
  }

				if v, ok := columnType.Unique(); !sqlserver && (!ok || !v) {
					t.Fatalf("column code2 unique should be correct, name: %v, column: %#v", columnType.Name(),
						columnType)
				}
			case "code3":
				// TODO
				// if v, ok := columnType.Unique(); !ok || v {
				// 	t.Fatalf("column code unique should be correct, name: %v, column: %#v", columnType.Name(), columnType)
				// }
			}
		}
	}

      int expectedSize) {
    return new CompactLinkedHashSet<>(expectedSize);
  }

  private static final int ENDPOINT = -2;

  // TODO(user): predecessors and successors should be collocated (reducing cache misses).
  // Might also explore collocating all of [hash, next, predecessor, successor] fields of an

    CharSource concatenated = CharSource.concat(cycle);

    String expected = "abcdabcd";

    // read the first 8 chars manually, since there's no equivalent to ByteSource.slice
    // TODO(cgdecker): Add CharSource.slice?
    StringBuilder builder = new StringBuilder();
    Reader reader = concatenated.openStream(); // no need to worry about closing
    for (int i = 0; i < 8; i++) {

   */
  private void assertSuppressed(Suppression... expected) {
    assertEquals(ImmutableList.copyOf(expected), suppressor.suppressions);
  }

  // TODO(cpovirk): Just use addSuppressed+getSuppressed now that we can rely on it.
  /** Suppressor that records suppressions. */
  private static class TestSuppressor implements Closer.Suppressor {

   *
   * <p>To represent decimal constants less than {@code 2^63}, consider {@link #valueOf(long)}
   * instead.
   *
   * @since 14.0
   */
  public static UnsignedLong fromLongBits(long bits) {
    // TODO(lowasser): consider caching small values, like Long.valueOf
    return new UnsignedLong(bits);
  }

  /**
   * Returns an {@code UnsignedLong} representing the same value as the specified {@code long}.
   *

 */
@GwtCompatible
@SuppressWarnings("serial") // uses writeReplace(), not default serialization
final class RegularImmutableBiMap<K, V> extends ImmutableBiMap<K, V> {
  @SuppressWarnings("unchecked") // TODO(cpovirk): Consider storing Entry<?, ?>[] instead.
  static final RegularImmutableBiMap<Object, Object> EMPTY =
      new RegularImmutableBiMap<>(
          null, null, (Entry<Object, Object>[]) ImmutableMap.EMPTY_ENTRY_ARRAY, 0, 0);

    reject.set(false);
    executor.execute(task);
    assertEquals(1, numCalls.get());
  }

  /*
   * Under Android, MyError propagates up and fails the test?
   *
   * TODO(b/218700094): Does this matter to prod users, or is it just a feature of our testing
   * environment? If the latter, maybe write a custom Executor that avoids failing the test when it
   * sees an Error?
   */