write-ui-tests

name	write-ui-tests
description	Creates UI tests for a GitHub issue and verifies they reproduce the bug. Iterates until tests actually fail (proving they catch the issue). Use when PR lacks tests or tests need to be created for an issue.
metadata	{"author":"dotnet-maui","version":"1.1"}
compatibility	Requires git, PowerShell, .NET SDK, and Appium for UI test execution.

Write UI Tests Skill

Creates UI tests that reproduce a GitHub issue, following .NET MAUI conventions. Verifies the tests actually fail before completing.

🛑 BLOCKING REQUIREMENT

YOU CANNOT COMPLETE THIS SKILL UNTIL TESTS FAIL.

A test that passes does NOT prove it catches the bug. You MUST:

1. Run tests and observe them FAIL
2. If tests pass, iterate on test code until they fail
3. Never report "done" with passing tests

If tests keep passing after 3 iterations:

• STOP and ask user: "Tests are passing but they should fail to prove they catch the bug. The test scenario may not correctly reproduce the issue. Should I try a different approach?"

Common mistakes that lead to passing tests:

• Test scenario doesn't match issue reproduction steps
• Checking wrong element or property
• Bug only manifests on specific platform (try different platform)
• Bug requires specific timing or async behavior not captured
• Issue description is incomplete - may need to ask user for clarification

When to Use

• ✅ PR has no tests and needs them
• ✅ Issue needs a reproduction test before fixing
• ✅ Existing tests don't adequately cover the bug

Required Input

Before invoking, ensure you have:

• Issue number (e.g., 33331)
• Issue description or reproduction steps
• Platforms affected (iOS, Android, Windows, MacCatalyst)

Platform selection guidance:

• Start with the platform mentioned in the issue (often in title or labels)
• If issue says "iOS" or has platform/iOS label → test on iOS first
• If issue says "Android" or has platform/Android label → test on Android first
• If issue affects "All" platforms → start with Android (faster emulator boot)
• If test passes on one platform, try another before concluding test is wrong

Workflow

Step 1: Read the UI Test Guidelines

cat .github/instructions/uitests.instructions.md

This contains the authoritative conventions for:

• File naming (IssueXXXXX.cs for C#-only, or IssueXXXXX.xaml/.xaml.cs for XAML)
• File locations (TestCases.HostApp/Issues/, TestCases.Shared.Tests/Tests/Issues/)
• Required attributes ([Issue()], [Category()])
• Test patterns and assertions

Step 2: Create HostApp Page

Location: src/Controls/tests/TestCases.HostApp/Issues/IssueXXXXX.cs

namespace Maui.Controls.Sample.Issues;

[Issue(IssueTracker.Github, XXXXX, "Brief description of issue", PlatformAffected.All)]
public partial class IssueXXXXX : ContentPage
{
    public IssueXXXXX()
    {
        // Create UI that reproduces the issue
        var button = new Button 
        { 
            Text = "Test Button",
            AutomationId = "TestButton"  // Required for Appium
        };
        
        var resultLabel = new Label
        {
            Text = "Waiting...",
            AutomationId = "ResultLabel"
        };
        
        button.Clicked += (s, e) => 
        {
            resultLabel.Text = "Success";
        };
        
        Content = new VerticalStackLayout
        {
            Children = { button, resultLabel }
        };
    }
}

Key requirements:

• Add AutomationId to all interactive elements
• Use [Issue()] attribute with tracker, number, description, platform
• Keep UI minimal - just enough to reproduce the bug

Note: XAML is optional. C#-only pages (as shown above) are simpler and preferred for most test scenarios. Use XAML only when the bug specifically relates to XAML parsing or markup behavior.

Step 3: Create NUnit Test

Location: src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/IssueXXXXX.cs

namespace Microsoft.Maui.TestCases.Tests.Issues;

public class IssueXXXXX : _IssuesUITest
{
    public override string Issue => "Brief description matching HostApp";

    public IssueXXXXX(TestDevice device) : base(device) { }

    [Test]
    [Category(UITestCategories.Button)]  // Pick ONE appropriate category
    public void ButtonClickUpdatesLabel()
    {
        // Wait for element to be ready
        App.WaitForElement("TestButton");

        // Interact with the UI
        App.Tap("TestButton");

        // Verify expected behavior
        var labelText = App.FindElement("ResultLabel").GetText();
        Assert.That(labelText, Is.EqualTo("Success"));
    }
}

Key requirements:

• Inherit from _IssuesUITest
• Use same AutomationId values as HostApp
• Add ONE [Category()] attribute (check UITestCategories.cs for options)
• Use App.WaitForElement() before interactions

Step 4: Verify Files Compile

# For Android
dotnet build src/Controls/tests/TestCases.HostApp/Controls.TestCases.HostApp.csproj -c Debug -f net10.0-android --no-restore -v q

# For iOS
dotnet build src/Controls/tests/TestCases.HostApp/Controls.TestCases.HostApp.csproj -c Debug -f net10.0-ios --no-restore -v q

# Test project (platform-independent)
dotnet build src/Controls/tests/TestCases.Shared.Tests/Controls.TestCases.Shared.Tests.csproj -c Debug --no-restore -v q

Step 5: Verify Tests Reproduce the Bug ⚠️ CRITICAL

Tests must FAIL to prove they catch the bug. Run verification:

pwsh .github/skills/verify-tests-fail-without-fix/scripts/verify-tests-fail.ps1 -Platform <platform> -TestFilter "IssueXXXXX"

Replace <platform> with android, ios, or maccatalyst based on the issue's affected platforms.

The script auto-detects that only test files exist (no fix files) and runs in "verify failure only" mode.

Why FAIL = success? The test must fail NOW (before the fix) to prove it catches the bug. After the fix is applied, it should pass. A test that passes now proves nothing.

If tests FAIL → ✅ Success! Tests correctly reproduce the bug. Proceed to Output.

If tests PASS → ❌ STOP. Test doesn't catch the bug. Iterate:

1. Re-read the issue reproduction steps - Is your test doing exactly what the issue describes?
2. Check if you're testing the right thing - Are you asserting on the correct element/property?
3. Try a different platform - Bug may only manifest on iOS vs Android
4. Add debug output - Use Console.WriteLine in HostApp to trace execution
5. Simplify - Remove complexity until you isolate the bug behavior
6. After 3 failed iterations, STOP and ask user:

   "Tests are passing after 3 iterations. This means either: (a) my test scenario doesn't correctly reproduce the bug, (b) the bug may already be fixed on this branch, or (c) I'm missing something from the issue description. How would you like me to proceed?"

Common reasons tests pass when they shouldn't:

Symptom	Likely Cause	Fix
Test passes on all attempts	Test scenario doesn't match bug	Re-read issue reproduction steps carefully
Test asserts pass but bug exists	Asserting wrong property/element	Check what exactly the bug affects
Works on Android, fails on iOS	Bug is platform-specific	Try both platforms
Bug involves timing	Race condition not captured	Add delays or event handlers
Bug involves navigation	Page lifecycle not exercised	Ensure pages are actually pushed/popped

Do NOT mark this skill complete until tests FAIL.

Output

⚠️ ONLY use this output format if tests FAIL. If tests pass, you have not completed this skill.

After completion (tests verified to fail), report:

✅ Tests created and verified for Issue #XXXXX

**Files:**
- `src/Controls/tests/TestCases.HostApp/Issues/IssueXXXXX.cs`
- `src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/IssueXXXXX.cs`

**Test method:** `ButtonClickUpdatesLabel`
**Category:** `UITestCategories.Button`
**Verification:** Tests FAIL as expected (bug reproduced)
**Failure message:** `Expected "X" but got "Y"` (include actual assertion failure)

If tests PASS after multiple iterations, report instead:

⚠️ Tests created but NOT verified for Issue #XXXXX

**Files:** [list files]
**Status:** Tests PASS when they should FAIL
**Iterations tried:** 3
**Problem:** [describe why test may not be catching the bug]
**Next steps:** Need guidance on reproduction steps

Common Patterns

Testing Property Changes

// HostApp: Add a way to trigger and observe the property
var picker = new Picker { AutomationId = "TestPicker" };
var statusLabel = new Label { AutomationId = "StatusLabel" };
picker.PropertyChanged += (s, e) => {
    if (e.PropertyName == nameof(Picker.IsOpen))
        statusLabel.Text = $"IsOpen={picker.IsOpen}";
};

// Test: Verify the property changes correctly
App.Tap("TestPicker");
App.WaitForElement("StatusLabel");
var status = App.FindElement("StatusLabel").GetText();
Assert.That(status, Does.Contain("IsOpen=True"));

Testing Layout/Positioning

// Test: Use GetRect() for position/size assertions
var rect = App.WaitForElement("TestElement").GetRect();
Assert.That(rect.Height, Is.GreaterThan(0));
Assert.That(rect.Y, Is.GreaterThanOrEqualTo(safeAreaTop));

Testing Visual State (Screenshots)

// Use retryTimeout for animations - keeps retrying until success
App.Tap("AnimatedButton");
VerifyScreenshot(retryTimeout: TimeSpan.FromSeconds(2));

// retryTimeout handles timing variance, small tolerance for cross-machine rendering
VerifyScreenshot(tolerance: 0.5, retryTimeout: TimeSpan.FromSeconds(2));

Testing Platform-Specific Behavior

// Only limit platforms when NECESSARY
[Test]
[Category(UITestCategories.Picker)]
public void PickerDismissResetsIsOpen()
{
    // This test should run on all platforms unless there's
    // a specific technical reason it can't
    App.WaitForElement("TestPicker");
    // ...
}

iOS Device Selection

When running tests on iOS, you may need to target a specific device or iOS version:

# Default: iPhone Xs with iOS 18.5
pwsh .github/scripts/BuildAndRunHostApp.ps1 -Platform ios -TestFilter "Issue12345"

# Find iPhone Xs with iOS 18.5 and get its UDID
UDID=$(xcrun simctl list devices available --json | jq -r '
  .devices | to_entries 
  | map(select(.key | contains("iOS-18-5"))) 
  | map(.value) | flatten 
  | map(select(.name == "iPhone Xs")) | first | .udid')

# Run with specific device
pwsh .github/scripts/BuildAndRunHostApp.ps1 -Platform ios -TestFilter "Issue12345" -DeviceUdid "$UDID"

Finding different device/version combinations:

# iPhone 16 Pro with any iOS version
UDID=$(xcrun simctl list devices available --json | jq -r '
  .devices[][] | select(.name == "iPhone 16 Pro") | .udid' | head -1)

# Any device with iOS 18.0
UDID=$(xcrun simctl list devices available --json | jq -r '
  .devices | to_entries 
  | map(select(.key | contains("iOS-18-0"))) 
  | map(.value) | flatten | .[0].udid')

Pre-Run Checklist

Before running verify-tests-fail.ps1, confirm:

• HostApp file exists: TestCases.HostApp/Issues/IssueXXXXX.cs
• NUnit test file exists: TestCases.Shared.Tests/Tests/Issues/IssueXXXXX.cs
• [Issue()] attribute present with all parameters
• All AutomationId values match between HostApp and test
• Test inherits from _IssuesUITest
• ONE [Category()] attribute from UITestCategories.cs

References

• Full conventions: .github/instructions/uitests.instructions.md
• Category list: src/Controls/tests/TestCases.Shared.Tests/UITestCategories.cs
• Example tests: src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/

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