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 { #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")
	}

    @DisplayName("MonotonicClock singleton instance should always return the same instance")
    void testSingletonInstance() {
        MonotonicClock clock1 = MonotonicClock.get();
        MonotonicClock clock2 = MonotonicClock.get();

        assertSame(clock1, clock2, "Multiple calls to get() should return the same instance");
    }

    @Test
    @DisplayName("MonotonicClock should always use UTC timezone")
    void testClockTimezone() {

    /**
     * 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.
     *

        // Project A should have the highest weight as it's at the root
        assertTrue(weightA > weightB, "Project A should have weight > Project B");
        assertTrue(weightA > weightC, "Project A should have weight > Project C");
        assertTrue(weightB > weightX, "Project B should have weight > Project X");
        assertTrue(weightC > weightX, "Project C should have weight > Project X");
    }

    @Test

        "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"
    )

        Plugin retrievedPlugin = project.getPlugin("org.apache.maven.plugins:maven-compiler-plugin");
        assertNotNull(retrievedPlugin, "Plugin should be found");
        assertEquals("3.8.1", retrievedPlugin.getVersion(), "Initial version should match");

        // Modify the plugin version
        retrievedPlugin.setVersion("3.11.0");

        // Verify the change persists when getting the plugin again

		t.Fatalf("value differs from expected")
	}
	if !ok {
		t.Fatalf("should be true")
	}

	if !lc.Contains("key1") {
		t.Fatalf("should contain key1")
	}
	if lc.Contains("key2") {
		t.Fatalf("should not contain key2")
	}

	v, ok = lc.Peek("key2")
	if v != "" {
		t.Fatalf("should be empty")
	}
	if ok {
		t.Fatalf("should be false")
	}

	if !reflect.DeepEqual(lc.Keys(), []string{"key1"}) {

                            null, "incomplete-project", null, "Should return null for missing groupId and version"),
                    Arguments.of("com.example", null, "1.0.0", "Should return null for missing artifactId"),
                    Arguments.of(null, null, "1.0.0", "Should return null for missing groupId and artifactId"),
                    Arguments.of("com.example", "test-project", null, "Should return null for missing version"),

    assert response.status_code == 422
    assert response.json() == {
        "detail": [
            {
                "type": "int_parsing",
                "loc": ["path", "item_id"],
                "msg": "Input should be a valid integer, unable to parse string as an integer",
                "input": "foobar",
            }
        ]
    }


def test_path_int_True():
    response = client.get("/path/int/True")