In this case, you could want to document how that external API *should* look like. What *path operation* it should have, what body it should expect, what response it should return, etc.

## An app with callbacks

Let's see all this with an example.

Imagine you develop an app that allows creating invoices.

These invoices will have an `id`, `title` (optional), `customer`, and `total`.

			t.Fatalf("Should find saved record")
		}
		return nil
	}); err != nil {
		t.Fatalf("no error should return, but got %v", err)
	}

	if err := DB.First(&User{}, "name = ?", user.Name).Error; err != nil {
		t.Fatalf("Should find saved record")
	}

	if err := DB.First(&User{}, "name = ?", user1.Name).Error; err == nil {
		t.Fatalf("Should not find rollbacked record")
	}

    /**
     * Indicates whether Maven should never fail the build, regardless of project result.
     *
     * @return an {@link Optional} containing true if the build should never fail, false if it should fail normally, or empty if not specified
     */
    @Nonnull
    Optional<Boolean> failNever();

    /**
     * Indicates whether Maven should resume from the last failed project in a previous build.
     *

 *             but should have been.
 *
 */
@Deprecated
public interface ProjectDependenciesResolver {

    /**
     * Resolves the transitive dependencies of the specified project.
     *
     * @param project         The project whose dependencies should be resolved, must not be {@code null}.
     * @param scopesToResolve The dependency scopes that should be resolved, may be {@code null}.

* `allow_origins` - A list of origins that should be permitted to make cross-origin requests. E.g. `['https://example.org', 'https://www.example.org']`. You can use `['*']` to allow any origin.
* `allow_origin_regex` - A regex string to match against origins that should be permitted to make cross-origin requests. e.g. `'https://.*\.example\.org'`.

  public void testGetOrDefault_present() {
    assertEquals(
        "getOrDefault(present, def) should return the associated value",
        v0(),
        getMap().getOrDefault(k0(), v3()));
  }

  @CollectionSize.Require(absent = ZERO)
  public void testGetOrDefault_presentNullDefault() {
    assertEquals(
        "getOrDefault(present, null) should return the associated value",
        v0(),
        getMap().getOrDefault(k0(), null));
  }

    assertSame(
        "toArray(sameSizeE[]) should return the given array", array, collection.toArray(array));
    expectArrayContentsAnyOrder(createSamplesArray(), array);
  }

  @CollectionFeature.Require(KNOWN_ORDER)
  public void testToArray_rightSizedArray_ordered() {
    E[] array = getSubjectGenerator().createArray(getNumElements());
    assertSame(

		t.Fatalf("no error should happen but got %v", err)
	}

	time.Sleep(time.Second)

	var result2 User
	if err := tx.Find(&result2, user.ID).Error; err != nil {
		t.Fatalf("no error should happen but got %v", err)
	}

	user2 := *GetUser("prepared_stmt2", Config{})
	if err := txCtx.Create(&user2).Error; err == nil {
		t.Fatalf("should failed to create with timeout context")
	}

    assertEquals("Cause should be available.", exception, handler.exception);
    assertEquals("EventBus should be available.", eventBus, handler.context.getEventBus());
    assertEquals("Event should be available.", EVENT, handler.context.getEvent());
    assertEquals("Subscriber should be available.", subscriber, handler.context.getSubscriber());
    assertEquals(
        "Method should be available.",

    assertEquals("Should be able to peek() at first element", "A", peekingIterator.peek());
    assertEquals(
        "Should be able to peek() first element multiple times", "A", peekingIterator.peek());
    assertEquals(
        "next() should still return first element after peeking", "A", peekingIterator.next());

    assertEquals("Should be able to peek() at middle element", "B", peekingIterator.peek());