Custom VPP apps: Integration Testing and Documentation

[cdcme]

Related user story

Parent: #32461
Research: #32713

Add comprehensive integration tests for custom VPP apps and update documentation to include instructions for custom app deployment.

Task

Current State:

• Integration tests mock iTunes API via appleITunesSrv httptest server
• No mock for VPP metadata proxy
• Feature guide covers public VPP apps only

Desired State:

• Integration tests mock VPP metadata proxy
• Tests verify custom apps work end-to-end
• Feature guide includes custom app instructions
• API documentation updated if needed

Conditions of satisfaction / implementation notes

Integration Test Infrastructure

• Mock VPP proxy server created (httptest.Server)
• Mock implements /register and /metadata endpoints
• FLEET_DEV_STOKEN_AUTHENTICATED_APPS_URL env var set in tests
• Mock can simulate custom apps (apps not in iTunes)
• Mock can simulate error scenarios (401, 429, 500)

Test Scenarios

• Custom app appears in GetAppStoreApps response
• Custom app can be added via API (AddAppStoreApp)
• Custom app can be added via GitOps (BatchAssociateVPPApps)
• Custom app can be installed on macOS host
• Custom app can be installed on iOS host
• Custom app can be installed on iPadOS host
• Custom app can be edited (self-service toggle)
• Custom app can be deleted
• Activity feed shows correct activities for custom apps
• Public apps still work (regression test)

Error Handling Tests

• Proxy unavailable - graceful error message
• Invalid license - clear error message
• Rate limited - retry behavior
• Custom app not in VPP account (when attempting to add by ID) - appropriate error

Documentation

• Feature guide updated: install-app-store-apps.md
• Add section on custom apps from Apple Business Manager
• Include prerequisites (app must be added to ABM first)
• Include troubleshooting tips for common issues
• API documentation unchanged (same endpoints work)