mstest-mvvm-testing-patterns

# MVVM Testing Patterns Agent validates MVVM behavior through focused MSTest v4 coverage for observable state, commands, async flows, validation, messaging, navigation, and service-backed workflows. ## When to Use | Condition | Use | |---|---| | Agent adds or changes view-model logic in WPF, WinUI, MAUI, or toolkit-based MVVM code. | Agent uses this skill. | | Agent needs regression coverage for `PropertyChanged`, command guards, or async commands. | Agent uses this skill. | | Agent tests navigation, messenger interactions, or validation-driven command readiness. | Agent uses this skill. | | Agent measures view-model coverage with MSTest v4 and repository patterns. | Agent uses this skill. | ## When Not to Use | Condition | Route | |---|---| | Agent tests rendering, layout, or accessibility behavior only. | Agent uses a UI automation or screen-focused skill. | | Agent tests Web API endpoints, handlers, or DTO validators. | Agent uses the matching backend testing skill. | | Agent needs a broad suite audit with no implementation work. | Agent uses a testing audit skill. | | Agent changes only passive models with no MVVM behavior. | Agent uses general unit testing guidance. | ## Required Inputs | Input | Required | Notes | |---|---|---| | Target view model | Yes | Identify state, commands, and collaborators. | | Expected behavior | Yes | Identify notifications, command gates, and side effects. | | Dependency seams | Yes | Identify services, repositories, messenger, and navigation boundaries. | | Coverage scope | No | Identify unit, integration, or coverage collection targets. | ## Workflow | Step | Agent Action | Test | Pass | |---|---|---|---| | 1 | Agent reads the target view model and sibling tests to match local naming and fixture patterns. | Review neighboring tests. | New tests align with repository conventions. | | 2 | Agent maps observable behaviors: property changes, command paths, validation, messaging, navigation, and async state. | Review the test map. | Each changed behavior has a test target. | | 3 | Agent selects the smallest isolation boundary for each collaborator. | Review fakes and mocks. | Setup stays concise and behavior-focused. | | 4 | Agent writes MSTest v4 tests for happy, edge, and failure paths through the public surface. | Run targeted tests. | Public behavior coverage stays balanced. | | 5 | Agent runs targeted coverage collection when the repository already uses coverage tooling. | Collect coverage for the target project. | View-model coverage runs complete successfully. | ## Test Strategy Matrix | Behavior | Agent pattern | Pass | |---|---|---| | Property change notification | Subscribe to `PropertyChanged` and capture changed member names. | Expected property names arrive in order. | | Command execution | Invoke the public command surface instead of private methods. | Expected state and collaborator effects occur. | | `CanExecute` guard | Toggle state around the guard condition and reevaluate commands. | Guard transitions match observable state. | | Async command | Await `ExecuteAsync`, inspect busy flags, and verify failure recovery. | Async state resets and outcomes stay deterministic. | | Validation logic | Drive invalid and valid inputs through the view-model surface. | Errors appear and clear predictably. | | Messaging and navigation | Use deterministic recipients and fake navigation seams. | Message interactions and route requests match expectation. | ## Isolation Matrix | Dependency shape | Agent default | Agent avoids | |---|---|---| | Remote services | Mocks or deterministic fakes | Live infrastructure in unit tests | | Navigation | Fake route and payload recorder | Shell or frame globals | | Messenger | `WeakReferenceMessenger` test setup or a focused fake bus | Cross-test shared singleton state | | DI container | Real `ServiceCollection` only for composition-sensitive checks | Container bootstrapping in simple unit tests | ## Reference Files | File | Purpose | |---|---| | [references/testing-examples.md](references/testing-examples.md) | Example tests, coverage details, integration hooks, MCP hooks, pitfalls, and outputs. | ## Verification Checklist | Check | Test | Pass | |---|---|---| | Notification coverage | Run notification-focused tests. | Expected property names raise correctly. | | Command coverage | Execute sync and async command tests. | State and collaborator effects match intent. | | Validation coverage | Run invalid and valid state tests. | Errors and command gates stay synchronized. | | Messaging coverage | Publish or receive through the configured messenger path. | Message interactions fire exactly once per scenario. | | Isolation quality | Review test doubles and cleanup. | Tests stay independent and order-insensitive. | | Coverage command | Run the targeted coverage command when applicable. | Coverage collection completes successfully. |