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`.

            assertTrue(result.success(), "Orchestrator should succeed");
            assertEquals(2, result.processedPoms().size(), "Should aggregate processed POMs");
            assertEquals(2, result.modifiedPoms().size(), "Should aggregate modified POMs");
            assertEquals(0, result.errorPoms().size(), "Should have no errors");
        }

        @Test
        @DisplayName("should handle strategy failures gracefully")

            assertTrue(result.contains("    <build>"), "Build element should be properly indented");
            assertTrue(result.contains("        <plugins>"), "Plugins element should be properly indented");
            assertTrue(result.contains("            <plugin>"), "Plugin element should be properly indented");
        }

        @Test
        @DisplayName("should format pluginManagement with proper indentation when added")

            // groupId should also be removed (can be inferred from project)
            assertNull(DomUtils.findChildElement(dependency, "groupId"));
            // artifactId should remain (always required)
            assertNotNull(DomUtils.findChildElement(dependency, "artifactId"));
        }

        @Test
        @DisplayName("should keep dependency version for external artifact")

        assertFalse(options.all().isPresent(), "--all should not be present by default");
        assertFalse(options.infer().isPresent(), "--infer should not be present by default");
        assertFalse(options.model().isPresent(), "--fix-model should not be present by default");
        assertFalse(options.model().isPresent(), "--model should not be present by default");

        // But the goal should be present

        "not used parameters should not be included"
    )
    assert '"syntaxHighlight": {"theme": "obsidian"}' in response.text, (
        "parameters with middle dots should be included in a JSON compatible way"
    )
    assert '"dom_id": "#swagger-ui"' in response.text, (
        "default configs should be preserved"
    )
    assert "presets: [" in response.text, "default configs should be preserved"

            assertTrue(result.success(), "Result should be successful when no errors");
            assertEquals(2, result.processedCount(), "Should have 2 processed POMs");
            assertEquals(1, result.modifiedCount(), "Should have 1 modified POM");
            assertEquals(1, result.unmodifiedCount(), "Should have 1 unmodified POM");
            assertEquals(0, result.errorCount(), "Should have no errors");
        }

        @Test

        assertTrue(nameIndex > 0, "Should contain name element");
        assertTrue(descriptionIndex > 0, "Should contain description element");
        assertTrue(propertiesIndex > 0, "Should contain properties element");

        // According to ELEMENT_ORDER: name should come before description, and properties should come much later
        assertTrue(nameIndex < descriptionIndex, "name should come before description");

        assertTrue(resource.getIncludes().contains("*.xml"), "Should contain *.xml");
        assertTrue(resource.getIncludes().contains("*.properties"), "Should contain *.properties");

        // Verify persistence
        Resource resourceAfter = project.getResources().get(0);
        assertEquals(2, resourceAfter.getIncludes().size(), "Should still have two includes");

			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")
	}