devjarus/ios-testing-debugging

iOS Testing & Debugging

Testing and debugging iOS apps using MCP servers (XcodeBuildMCP + ios-simulator-mcp), Xcode CLI tools, and test frameworks.

When to Apply

• Building and testing iOS apps
• Managing iOS simulators (boot, install, launch, screenshot)
• Writing XCTest or Swift Testing unit tests
• Writing XCUITest UI automation tests
• Debugging crashes, memory leaks, layout issues
• Verifying UI flows on simulator

MCP Servers Available

Two MCP servers are configured in .mcp.json for iOS development:

XcodeBuildMCP (mcp__xcodebuild__*)

The primary tool for building, testing, and debugging:

• Build: xcodebuild_build — build project/workspace for simulator or device
• Test: xcodebuild_test — run unit and UI test suites
• Debug: xcodebuild_debug — attach LLDB, set breakpoints, inspect variables
• Resolve errors: build errors include fix suggestions; iterate automatically

ios-simulator-mcp (mcp__ios-simulator__*)

Simulator control and UI interaction:

• Screenshots: screenshot — capture current simulator screen
• UI inspection: ui_describe_all — get accessibility tree of entire screen
• Tap: ui_tap — tap at coordinates or element
• Type: ui_type — input text into focused field
• Swipe: ui_swipe — swipe gestures
• Point inspection: ui_describe_point — get element at coordinates
• View: ui_view — compressed screenshot as base64
• Video: record_video / stop_recording — capture interaction videos
• App lifecycle: install_app, launch_app — install and launch on simulator

Testing Workflow

For Evaluator (verifying iOS apps)

1. Build the app — use XcodeBuildMCP to build for simulator
2. Boot simulator — use xcrun simctl boot via Bash or MCP
3. Install and launch — use ios-simulator-mcp install_app + launch_app
4. Inspect UI — ui_describe_all to get accessibility tree
5. Test flows — ui_tap, ui_type, ui_swipe to interact
6. Screenshot evidence — screenshot at each step for review.md
7. Run test suite — use XcodeBuildMCP to run XCTest/XCUITest
8. Clean up — xcrun simctl shutdown all

For Implementor (writing tests)

1. Unit tests first (TDD):

   • XCTest: XCTAssertEqual, XCTAssertTrue, XCTAssertThrowsError
   • Swift Testing (iOS 16+): @Test, #expect, #require, @Suite
   • Test ViewModels and business logic — not view hierarchy
   • Mock dependencies via protocol conformance

2. UI tests for critical flows:

   • XCUITest: XCUIApplication().launch(), query by accessibility identifier
   • Interact: .tap(), .typeText(), .swipeUp()
   • Assert: .exists, .waitForExistence(timeout:)

3. Build and run — use XcodeBuildMCP from CLI

Fallback: CLI Commands (rules/cli-fallback.md)

When MCP servers aren't available, use Bash directly:

# List simulators
xcrun simctl list devices available

# Boot and install
xcrun simctl boot "iPhone 16"
xcrun simctl install booted ./build/MyApp.app
xcrun simctl launch booted com.example.MyApp

# Screenshot
xcrun simctl io booted screenshot /tmp/screen.png

# Build and test
xcodebuild test -scheme MyApp -sdk iphonesimulator \
  -destination 'platform=iOS Simulator,name=iPhone 16'

# Clean up
xcrun simctl shutdown all

Debugging (rules/debugging.md)

• XcodeBuildMCP LLDB — attach debugger, set breakpoints, inspect variables via MCP
• Console.app — filter by app process for os_log/print output
• Instruments — Time Profiler, Allocations, Leaks, Network
• Memory Graph — detect retain cycles and leaks

Rules

1. Prefer MCP tools over raw CLI — XcodeBuildMCP and ios-simulator-mcp provide structured output
2. Always clean up simulators — shutdown after testing to free resources
3. Use accessibility identifiers — not labels for element queries (labels change with localization)
4. Test on multiple sizes — iPhone SE, iPhone 16, iPad
5. Mock network in unit tests — use URLProtocol stubbing, not real API calls
6. Screenshot on failure — capture simulator state for debugging
7. Never hardcode simulator UDIDs — query by name/type