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")
	}

                    "msg": "Input should be a valid boolean, unable to interpret input",
                    "input": "foobar",
                }
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1
        {
            "detail": [
                {
                    "loc": ["path", "item_id"],
                    "msg": "value could not be parsed to a boolean",

    /**
     * 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.
     *

* There should be tests testing the source example.
* Before the PR is applied, the new tests should fail.
* After applying the PR, the new tests should pass.
* Coverage should stay at 100%.

    ), "overridden configs should be preserved"
    assert (
        '"deepLinking": true' not in response.text
    ), "overridden configs should not include the old value"
    assert (
        '"syntaxHighlight": false' not in response.text
    ), "not used parameters should not be included"
    assert (
        '"dom_id": "#swagger-ui"' in response.text
    ), "default configs should be preserved"

	} else if user.ID == 0 {
		t.Fatalf("user's primary value should not zero, %v", user.ID)
	} else if user.UpdatedAt.IsZero() {
		t.Fatalf("user's updated at should not zero, %v", user.UpdatedAt)
	}
	lastUpdatedAt = user.UpdatedAt

	if err := DB.Model(user).Update("Age", 10).Error; err != nil {
		t.Errorf("errors happened when update: %v", err)
	} else if user.Age != 10 {
		t.Errorf("Age should equals to 10, but got %v", user.Age)
	}

		t.Fatalf("Scan into struct should work, got %#v, should %#v", res, user3)
	}

	DB.Table("users").Select("id, name, age").Where("id = ?", user2.ID).Scan(&res)
	if res.ID != user2.ID || res.Name != user2.Name || res.Age != int(user2.Age) {
		t.Fatalf("Scan into struct should work, got %#v, should %#v", res, user2)
	}

	if DB.Where("sdsd.zaaa = ?", "sd;;;aa").Pluck("aaa", &columns).Error == nil {
		t.Errorf("Should got error with invalid SQL")
	}

	if DB.Model(&User{}).Where("sdsd.zaaa = ?", "sd;;;aa").Pluck("aaa", &columns).Error == nil {
		t.Errorf("Should got error with invalid SQL")
	}

	if DB.Where("sdsd.zaaa = ?", "sd;;;aa").Find(&User{}).Error == nil {
		t.Errorf("Should got error with invalid SQL")
	}

	var count1, count2 int64

		t.Errorf("name should be groupby, but got %v, total should be 60, but got %v", name, total)
	}

	if err := DB.Model(&User{}).Select("name, sum(age) as total").Where("name LIKE ?", "groupby%").Group("name").Having("name = ?", "groupby1").Row().Scan(&name, &total); err != nil {
		t.Errorf("no error should happen, but got %v", err)
	}

	if name != "groupby1" || total != 660 {