Add --enable-coverage flag for code coverage collection from device tests

[amirvenus]

Summary

Adds an optional --enable-coverage CLI flag across all platforms that enables code coverage collection during XHarness device test execution. When enabled, XHarness generates a Cobertura XML coverage report and places it in the output directory alongside test results.

No external coverage tools (coverlet, etc.) are required. CoverageManager generates method-level coverage by reflecting over the loaded test assemblies. Standard tools like coverlet.msbuild cannot instrument assemblies for device builds (APK/app bundles) since they only hook into the dotnet test pipeline — CoverageManager solves this by providing built-in coverage that works on all platforms.

If an external tool has already produced a coverage file at the expected path, CoverageManager uses that file instead.

Addresses #1135.

What's included

• --enable-coverage CLI flag on all platform commands:

  • android test, android run
  • apple test, apple just-test
  • wasm test, wasm test-browser

• Test Runner integration (TestRunners.Common):

  • NUNIT_ENABLE_COVERAGE / NUNIT_COVERAGE_OUTPUT_PATH environment variable support in ApplicationOptions
  • CoverageManager that generates method-level Cobertura XML via reflection over loaded test assemblies (no external dependencies)
  • Coverage lifecycle integrated into ApplicationEntryPoint.InternalRunAsync()

• Per-platform transport:

  • Android: Coverage flag passed as instrumentation argument → test app bridges to env var → CoverageManager generates report → path reported via INSTRUMENTATION_RESULT: coverage-results-path=<path> → InstrumentationRunner pulls file from device via adb
  • Apple (iOS/tvOS/macOS): NUNIT_ENABLE_COVERAGE injected as env var via the orchestrator → coverage file written to app's Documents directory → pulled alongside test results
  • WASM: Coverage data emitted on stdout using STARTCOVERAGEXML <len> <base64> ENDCOVERAGEXML markers → WasmTestMessagesProcessor decodes and writes to output directory

• ThreadlessXunitTestRunner made public: Enables Android test apps to use the runner that works with .NET Android's assembly store (in-memory test discovery via ReflectionAssemblyInfo, no .dll file on disk required)

Usage

# Android
xharness android test --app=test.apk --package-name=com.example --enable-coverage --output-directory=./out

# iOS
xharness apple test --app=TestApp.app --target=ios-simulator-64 --enable-coverage --output-directory=./out

# WASM
xharness wasm test --enable-coverage --output-directory=./out -- test.js

After the run, coverage.cobertura.xml appears in the output directory. The file uses standard Cobertura format consumable by Azure DevOps, Codecov, ReportGenerator, etc.

Test plan

• Unit tests for CoverageManager (8 tests) — constructor, path resolution, env var setting, reflection coverage generation, fallback behavior
• All existing unit tests pass (97 TestRunners + 21 Android = 118 tests)
• Android end-to-end: Built test APK with Android.OS.Build API tests → deployed to emulator via locally-built XHarness CLI with --enable-coverage → 5/5 tests passed → coverage.cobertura.xml (2,741 bytes) pulled from device to output directory
• iOS end-to-end: Built iOS app with UIKit.UIDevice API tests → ran on iPhone 11 Pro simulator (iOS 26.2) via locally-built XHarness CLI with --enable-coverage → 6/6 tests passed → coverage.cobertura.xml generated in app container
• CLI builds successfully for all platforms

🤖 Generated with Claude Code

[amirvenus]

The 2 failing checks (E2E Apple - iOS devices and E2E Apple - tvOS devices) are pre-existing failures on main — the ios-device-System.Buffers.Tests.app Helix work item fails identically on the main branch. These are infrastructure/device-lab issues, not related to this PR.

All 12 checks relevant to our changes pass: builds (Windows/OSX, Debug/Release), Android E2E (devices, simulators, manual commands), Apple E2E (simulators, simulator commands, device commands), and WASM E2E.