Uno Testing Assertions

Uno Platform Test Assertions Skill

Prerequisite: This skill requires the Uno App MCP (the uno_app_* tools), provided by the Uno tooling. It is a separate server from the documentation MCP used by other skills. Before proceeding, confirm the uno_app_* tools are available; if they are not, stop and tell the user to enable the Uno tooling rather than attempting to test without them.

This skill provides patterns for validating UI state and asserting test conditions when testing Uno Platform applications with the Uno App MCP tools.

Assertion Types

Visual Assertions (Screenshots)

Use uno_app_get_screenshot to capture visual state:

uno_app_get_screenshot(fileType: "png", quality: 100, path: "/path/to/screenshot.png")

Validation approaches:

1. Visual comparison: Compare with baseline images
2. Manual review: Save screenshots for human inspection
3. AI-assisted validation: Describe expected visual state and verify

Structure Assertions (Visual Tree)

Use uno_app_visualtree_snapshot to verify UI structure:

Assert element exists:

• Get visual tree snapshot
• Search for element by name, AutomationId, or type
• Fail if element not found

Assert element not visible:

• Get tree with includeHidden: false
• Verify element is NOT in the returned tree

Assert element visible:

• Get tree with includeHidden: false
• Verify element IS in the returned tree

Property Assertions

From visual tree, check element properties:

Data Assertions

Use uno_app_get_element_datacontext to validate bound data:

uno_app_get_element_datacontext(elementRef: "element_handle")

Verify:

• ViewModel property values
• Collection counts and items
• Computed properties
• State flags

Common Assertion Patterns

Assert Page Loaded

1. uno_app_visualtree_snapshot(justMyCode: true)
2. Search for expected page/view element
3. Verify page-specific elements exist
4. Optionally capture screenshot for visual confirmation

Assert Button State

1. uno_app_visualtree_snapshot(justMyCode: true)
2. Find button by name or AutomationId
3. Check IsEnabled property
4. Verify Content matches expected text

Assert Text Content

1. uno_app_visualtree_snapshot(justMyCode: true)
2. Find TextBlock/TextBox element
3. Verify Text property matches expected value

Assert List Items

1. uno_app_visualtree_snapshot(justMyCode: true)
2. Find ListView/ItemsRepeater element
3. Count child items
4. Verify expected count
5. Check item content if needed

Assert Dialog Displayed

1. uno_app_visualtree_snapshot(justMyCode: true)
2. Search for ContentDialog or Popup element
3. Verify dialog-specific content exists
4. Capture screenshot for visual confirmation

Assert Form Validation Errors

1. Enter invalid data in form
2. Attempt to submit
3. uno_app_visualtree_snapshot(justMyCode: true)
4. Look for validation error TextBlocks
5. Verify error messages match expected text

Assert Navigation Occurred

1. Trigger navigation action
2. uno_app_visualtree_snapshot(justMyCode: true)
3. Verify previous page elements are gone
4. Verify new page elements are present

Screenshot-Based Assertions

Capturing for Comparison

uno_app_get_screenshot(
  fileType: "png",
  quality: 100,
  path: "/tests/screenshots/test_case_name.png"
)

Assertion Strategies

Pixel-perfect comparison:

• Use when UI is deterministic
• Be aware of anti-aliasing differences
• May need tolerance threshold

Region comparison:

• Compare specific areas of interest
• Ignore dynamic content regions
• Focus on stable UI elements

Semantic comparison:

• Describe what should be visible
• Verify key visual elements
• Allow for minor variations

Handling Dynamic Content

When screenshots contain dynamic data:

1. Use data mocking/seeding
2. Focus assertions on static elements
3. Mask dynamic regions
4. Use structural validation instead

Data Context Assertions

Verify ViewModel State

1. Get element handle from visual tree
2. uno_app_get_element_datacontext(elementRef: "handle")
3. Parse returned XML
4. Assert property values match expected state

Example Assertions

Assert user is logged in:

• Get DataContext of user info element
• Verify IsLoggedIn: true
• Verify Username has value

Assert item count:

• Get DataContext with collection property
• Verify collection count matches expected

Assert computed state:

• Get DataContext after action
• Verify derived/computed properties updated

Timing and Retry Patterns

Wait for Condition

When UI updates asynchronously:

Loop (max N attempts):
  1. Get visual tree snapshot
  2. Check for expected condition
  3. If condition met, break
  4. Wait brief interval
  5. Retry
Fail if condition not met after all attempts

Wait for Element

Retry up to 10 times:
  1. uno_app_visualtree_snapshot(justMyCode: true)
  2. Search for expected element
  3. If found, return success
  4. Wait 500ms
  5. Retry
Fail with "Element not found" if all retries exhausted

Wait for Loading Complete

Retry until no loading indicators:
  1. uno_app_visualtree_snapshot(justMyCode: true)
  2. Search for ProgressRing, ProgressBar, loading text
  3. If none found, loading complete
  4. Wait 500ms
  5. Retry

Failure Handling

Capture Diagnostic Info

On assertion failure:

1. Capture screenshot for visual debugging
2. Get full visual tree (justMyCode: false)
3. Log expected vs actual values
4. Save DataContext if relevant

Common Failure Causes

Test Organization Tips

Before Each Test

1. Ensure app is running: uno_app_get_runtime_info
2. Navigate to known initial state
3. Clear any persistent test data

After Each Test

1. Capture final screenshot (pass or fail)
2. Reset app state if possible
3. Log assertion results

On Failure

1. Capture diagnostic screenshot
2. Dump visual tree
3. Save DataContext of relevant elements
4. Preserve failure artifacts for debugging

Best Practices

1. Be specific: Assert on exact values, not just existence
2. Use proper identifiers: Rely on AutomationId over generated names
3. Handle timing: Always account for async operations
4. Capture evidence: Screenshots on both pass and fail
5. Test independence: Each test should set up its own state
6. Meaningful messages: Include context in failure messages