Add comprehensive test parallelization analysis document

Co-authored-by: tig <[email protected]>

Tests/TEST_PARALLELIZATION_ANALYSIS.md

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+# Test Parallelization Analysis
+
+## Summary
+
+This document provides an analysis of the test parallelization effort for Terminal.Gui. The goal is to identify tests in `UnitTests` that can be moved to `UnitTests.Parallelizable` and remove duplicates.
+
+## Key Findings
+
+### Test Counts
+- **UnitTests**: ~1446 tests (1213 Fact, 233 Theory) across 140 files
+- **UnitTestsParallelizable**: ~1437 tests (1078 Fact, 359 Theory) across 142 files
+- **Tests using [AutoInitShutdown]**: 452
+- **Tests using [SetupFakeDriver]**: 206
+
+### What Prevents Parallelization
+
+Tests cannot be parallelized if they:
+1. Use `[AutoInitShutdown]` - requires `Application.Init/Shutdown` which creates global state
+2. Use `[SetupFakeDriver]` - sets `Application.Driver` which is global
+3. Call `Application.Init()` directly
+4. Modify `ConfigurationManager` global state (Enable/Load/Apply/Disable)
+5. Modify static properties like `Key.Separator`, `CultureInfo.CurrentCulture`, etc.
+6. Use `Application.Top`, `Application.Driver`, `Application.MainLoop` or other singleton state
+7. Are integration tests that test multiple components working together
+
+### Test Files Analysis
+
+#### Files Without AutoInitShutdown or SetupFakeDriver (49 files)
+
+Many of these still cannot be parallelized because they use global state:
+
+**Configuration Tests (8 files)**:
+- `SchemeManagerTests.cs` - Uses ConfigurationManager.Enable/Disable - NOT parallelizable
+- `ConfigPropertyTests.cs` - Different from Parallelizable version, complementary
+- `AppScopeTests.cs` - Needs analysis
+- `ThemeManagerTests.cs` - Uses ConfigurationManager - NOT parallelizable
+- `KeyJsonConverterTests.cs` - Different from Parallelizable version
+- `ThemeScopeTests.cs` - Different from Parallelizable version
+- `GlyphTests.cs` - Uses ConfigurationManager - NOT parallelizable
+- `ConfigurationMangerTests.cs` - Different from Parallelizable version
+- `SettingsScopeTests.cs` - Different from Parallelizable version
+
+**Input Tests (1 file)**:
+- `KeyTests.cs` - Modifies `Key.Separator` static property with comment noting it can't be parallelized - CANNOT BE MOVED
+
+**Application Tests (7 files)**:
+- `MainLoopTests.cs` - Needs analysis
+- `MainLoopCoordinatorTests.cs` - Needs analysis
+- `StackExtensionsTests.cs` - **MOVED TO PARALLELIZABLE** ✅
+- `ApplicationPopoverTests.cs` - Needs analysis
+- `ApplicationMouseEnterLeaveTests.cs` - Needs analysis
+- `MainLoopTTests.cs` - Needs analysis
+- `ApplicationImplTests.cs` - Needs analysis
+
+**View/Component Tests (8 files)**:
+- `SliderTests.cs` - Needs analysis
+- `Menuv1Tests.cs` - Likely uses Application state
+- `TabTests.cs` - Needs analysis
+- `TimeFieldTests.cs` - Needs analysis
+- `TextValidateFieldTests.cs` - Needs analysis
+- `HexViewTests.cs` - Needs analysis
+- `ViewCommandTests.cs` - Different from Parallelizable, complementary
+- `ViewportSettings.TransparentMouseTests.cs` - Needs analysis
+
+**View Internal Tests (6 files)**:
+- `AdornmentSubViewTests.cs` - Needs analysis
+- `DiagnosticsTests.cs` - Needs analysis
+- `Dim.FillTests.cs` - Needs analysis
+- `Pos.ViewTests.cs` - Needs analysis
+- `Pos.Tests.cs` - Needs analysis
+- `GetViewsUnderLocationTests.cs` - Needs analysis
+
+**Console Driver Tests (13 files)**:
+- `MainLoopDriverTests.cs` - Needs analysis
+- `AnsiKeyboardParserTests.cs` - Needs analysis
+- `ConsoleDriverTests.cs` - Creates driver instances, likely NOT parallelizable
+- `DriverColorTests.cs` - Needs analysis
+- `ConsoleInputTests.cs` - Needs analysis
+- `ContentsTests.cs` - Needs analysis
+- `ClipRegionTests.cs` - Needs analysis
+- `NetInputProcessorTests.cs` - Needs analysis
+- `KeyCodeTests.cs` - Uses `Application.QuitKey` - NOT parallelizable
+- `MouseInterpreterTests.cs` - Needs analysis
+- `WindowSizeMonitorTests.cs` - Needs analysis
+- `AddRuneTests.cs` - Calls `driver.Init()` - likely NOT parallelizable
+- `AnsiResponseParserTests.cs` - Needs analysis
+- `WindowsInputProcessorTests.cs` - Needs analysis
+- `AnsiMouseParserTests.cs` - Needs analysis
+- `AnsiRequestSchedulerTests.cs` - Needs analysis
+- `ConsoleScrolllingTests.cs` - Needs analysis
+
+**Resource Tests (1 file)**:
+- `ResourceManagerTests.cs` - Modifies `CultureInfo.CurrentCulture` - NOT parallelizable
+
+**Other Tests (5 files)**:
+- `EscSeqRequestsTests.cs` - Needs analysis
+- Drawing tests mostly use AutoInitShutdown
+
+### Pattern Analysis
+
+**Complementary vs Duplicate Tests**:
+
+Most test files with the same name in both projects are **COMPLEMENTARY, NOT DUPLICATES**:
+- **UnitTests** typically contains integration tests that test components working with `Application`, drivers, and ConfigurationManager
+- **UnitTestsParallelizable** typically contains unit tests that test components in isolation without global state
+
+Examples:
+- `ThicknessTests.cs`:
+  - UnitTests: Tests `Draw()` method with Application.Driver (255 lines)
+  - Parallelizable: Tests constructors, properties, operators (619 lines)
+  
+- `ViewCommandTests.cs`:
+  - UnitTests: Tests Button clicks with Application mouse events
+  - Parallelizable: Tests Command pattern in isolation
+  
+- `ConfigPropertyTests.cs`:
+  - UnitTests: Tests Apply() with static properties
+  - Parallelizable: Tests concurrent access patterns
+
+## Completed Work
+
+✅ **StackExtensionsTests.cs** (10 tests, 195 lines)
+- Pure unit test of Stack extension methods
+- No dependencies on Application or ConfigurationManager
+- Successfully moved from UnitTests to UnitTestsParallelizable
+- All tests pass in parallelizable project
+
+## Recommendations
+
+### Immediate Actions
+1. Most tests in UnitTests should REMAIN there as they are integration tests
+2. Focus on identifying truly duplicated tests rather than moving tests
+3. Tests that modify global state cannot be parallelized
+
+### Long-term Strategy
+1. **Documentation**: Create clear guidelines on when tests belong in each project
+2. **Naming Convention**: Consider renaming to make the distinction clear (e.g., `IntegrationTests` vs `UnitTests`)
+3. **New Test Guidelines**: All new tests should be written for UnitTests.Parallelizable unless they require global state
+
+### Tests That MUST Stay in UnitTests
+- Any test using `[AutoInitShutdown]` or `[SetupFakeDriver]`
+- Any test that calls `Application.Init()` or `Application.Shutdown()`
+- Any test that uses `Application.Driver`, `Application.Top`, `Application.MainLoop`
+- Any test that modifies `ConfigurationManager` state
+- Any test that modifies static properties
+- Integration tests that test multiple components together
+
+### Candidates for Further Analysis
+The following files need deeper analysis to determine if they can be moved or have duplicates:
+- MainLoop related tests
+- Some View component tests that might not use global state
+- Some Console driver tests that might be pure unit tests
+
+## Scope Assessment
+
+Given the analysis:
+- ~1446 tests in UnitTests
+- 452 use [AutoInitShutdown]
+- 206 use [SetupFakeDriver]
+- Most remaining tests use Application or ConfigurationManager state
+
+**Estimate**: Only 5-10% of tests (50-150 tests) could potentially be moved to Parallelizable, and many of those already have complementary versions there. This is a massive undertaking that would require:
+- Detailed analysis of each of ~140 test files
+- Understanding the intent of each test
+- Determining if tests are duplicates or complementary
+- Rewriting tests to remove dependencies on global state where possible
+- Extensive testing to ensure nothing breaks
+
+This would easily be 40-80 hours of careful, methodical work.