Removes dependency on RemoteExecutor in tests

[ricardobossan]

Fixes #4500 (partial; see "Out of scope" below).

Supersedes #12379, which replaced RemoteExecutor.Invoke(...) with Task.Run(...).Wait(). That doesn't work for this set of tests: they mutate irreversible process-wide state (Application.EnableVisualStyles, Application.VisualStyleState, Application.CurrentCulture, Control.CheckForIllegalCrossThreadCalls), so any in-process replacement leaves the mutations behind for whatever runs next. The tests need a host that's isolated by construction.

This PR follows RussKie's suggestion on #4500: move tests that legitimately need an isolated, visual-styles-enabled host into UIIntegrationTests, which already runs serially (eng/xunit.runner.json: parallelizeTestCollections: false, maxParallelThreads: 1) and pre-enables visual styles via ControlTestBase.

Root Cause

The original skip reason on each test ("Crash with AbandonedMutexException. See: https://github.com/dotnet/arcade/issues/5325") blames RemoteExecutor, but arcade#5325 is actually a Coverlet bug (UnloadModule mutex); the winforms repo still consumes the affected coverlet.msbuild variant. RemoteExecutor isn't the bug; it's the side that was easy to remove. These tests need some form of isolation though; EnableVisualStyles is a one-way switch, and VisualStyleState writes broadcast WM_THEMECHANGED to every HWND in the process. UIIntegrationTests already provides that isolation by construction.

Proposed changes

• Migrate the 17 previously-skipped tests below from src/test/unit/System.Windows.Forms/... to src/test/integration/UIIntegrationTests/.... Each migrated test no longer needs RemoteExecutor and is no longer skipped.
• Remove the corresponding using Microsoft.DotNet.RemoteExecutor; and orphaned MemberData helpers from the unit-test files. using is preserved in ApplicationTests.cs because two non-skipped tests there still use RemoteExecutor (out of scope for this PR).
• Net: −616 / +33 lines under src/test/unit/, +672 lines under src/test/integration/UIIntegrationTests/ (six new files).

Migrated tests:

New file (UIIntegrationTests)	Migrated tests
Application.ParkingWindowTests.cs	ParkingWindow_DoesNotThrowOnGarbageCollecting
Application.StaticStateTests.cs	Application_CurrentCulture_Set_GetReturnsExpected, Application_EnableVisualStyles_InvokeBeforeGettingRenderWithVisualStyles_Success, Application_VisualStyleState_Set_ReturnsExpected
CommonDialogTests.cs	3× CommonDialog_ShowDialog_*WithVisualStyles_*
DataGridViewHeaderCellTests.cs	MouseLeaveUnsharesRow_InvokeWithDataGridViewMouseDown, OnMouseDown_InvalidRowIndexVisualStyles, OnMouseUp_InvalidRowIndexVisualStyles
ListViewInsertionMarkTests.cs	5× AppearsAfterItem_/Color_/Index_GetInsertMark[WithColor]_Success (unsafe, via LVM_GETINSERTMARK / LVM_GETINSERTMARKCOLOR)
TabPageTests.cs	BackColor_GetVisualStyles_ReturnsExpected, BackColor_GetVisualStylesWithParent_ReturnsExpected

Two intentional deltas from the original tests (both annotated inline):

1. Application_EnableVisualStyles_InvokeAfterGettingRenderWithVisualStyles_Success is dropped. Its precondition is UseVisualStyles == false followed by a call to EnableVisualStyles(). EnableVisualStyles is a one-way switch, and any test project that has previously enabled visual styles (which UIIntegrationTests does on startup) can never satisfy that precondition again. The behavior under test is documented as "not a recommended scenario"; the original only worked by spawning a fresh process.
2. Application_CurrentCulture_Set_GetReturnsExpected keeps every managed-side assertion but drops the Assert.Equal(expectedLcid, PInvokeCore.GetThreadLocale()) round-trip. UIIntegrationTests is decorated with [UseDefaultXunitCulture] (via ControlTestBase), and xunit's culture fixture restores the thread locale around test execution. SetThreadLocale also silently no-ops for some LCIDs (notably invariant 0x7F) on STA hosts. The Win32-level round-trip was an implementation detail that only held inside a freshly-spawned RemoteExecutor child; Application.CurrentCulture's documented surface is the managed Thread/CultureInfo pair, which is still verified.

Out of scope (follow-up)

Roughly 17 additional tests carry the same "AbandonedMutexException ... arcade#5325" skip reason but were not in #12379's scope: ~6 more in DataGridViewHeaderCellTests, 1 in ListViewTests, and ~10 in ListViewGroupTests. Per the staggered approach we discussed on the issue, leaving those for a follow-up PR keeps this one reviewable.

Customer Impact

• None. Test-only change. No product code is touched.

Regression?

• No.

Risk

• Minimal. The migration restores test coverage that was previously skipped; if anything regresses it can only surface as test failures (caught by CI before merge), not as customer-facing behavior. UIIntegrationTests already covers the same project surface.

Test methodology

• Unit tests / Integration tests. Built the solution locally; the migrated tests run green inside UIIntegrationTests. The unit-tests assembly still builds with the using/helper removals applied. No remaining references to the deleted MemberData helpers (CustomLCIDCultureInfo, BackColor_GetVisualStylesWithParent_TestData, MouseLeaveUnsharesRow_WithDataGridViewMouseDown_TestData); grep-verified before deletion.

Test environment(s)

• 11.0.100-preview.4.26210.111

Microsoft Reviewers: Open in CodeFlow

[KlausLoeffelmann]

@ricardobossan - can you check why the tests fail?

[ricardobossan]

Drafting until feedback is handled.

[ricardobossan]

@ricardobossan - can you check why the tests fail?

@KlausLoeffelmann The previous commit removed a using statement that shouldn't have been removed. Fixed it, and the tests are now passing. Ready for review. Thank you!

[Copilot]

Pull request overview

This PR migrates selected tests that depended on RemoteExecutor into UIIntegrationTests, reducing unit-test dependency on process isolation while preserving coverage for visual-styles and process-wide state scenarios.

Changes:

• Removes skipped RemoteExecutor-based tests and orphaned helpers/usings from unit test files.
• Adds migrated UI integration test files for Application, CommonDialog, DataGridViewHeaderCell, ListViewInsertionMark, and TabPage scenarios.
• Drops one visual-styles test that cannot be represented without fresh process isolation.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/test/unit/System.Windows.Forms/System/Windows/Forms/TabPageTests.cs	Removes skipped visual-styles TabPage tests and replaces them with migration comments.
src/test/unit/System.Windows.Forms/System/Windows/Forms/ListViewInsertionMarkTests.cs	Removes skipped visual-styles insertion mark tests and RemoteExecutor usage.
src/test/unit/System.Windows.Forms/System/Windows/Forms/DataGridViewHeaderCellTests.cs	Removes selected skipped DataGridViewHeaderCell tests and associated data helper.
src/test/unit/System.Windows.Forms/System/Windows/Forms/CommonDialogTests.cs	Removes skipped CommonDialog visual-styles tests and RemoteExecutor import.
src/test/unit/System.Windows.Forms/System/Windows/Forms/ApplicationTests.cs	Removes skipped process-wide Application state tests and related culture helper.
src/test/unit/System.Windows.Forms/System/Windows/Forms/Application.ParkingWindowTests.cs	Removes skipped ParkingWindow GC test and RemoteExecutor import.
src/test/integration/UIIntegrationTests/TabPageTests.cs	Adds migrated TabPage visual-styles coverage.
src/test/integration/UIIntegrationTests/ListViewInsertionMarkTests.cs	Adds migrated ListViewInsertionMark visual-styles/native message coverage.
src/test/integration/UIIntegrationTests/DataGridViewHeaderCellTests.cs	Adds migrated DataGridViewHeaderCell visual-styles mouse state coverage.
src/test/integration/UIIntegrationTests/CommonDialogTests.cs	Adds migrated CommonDialog visual-styles owner coverage.
src/test/integration/UIIntegrationTests/Application.StaticStateTests.cs	Adds migrated Application culture, visual styles, and visual style state coverage.
src/test/integration/UIIntegrationTests/Application.ParkingWindowTests.cs	Adds migrated ParkingWindow GC/cross-thread check coverage.

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[LeafShi1]

There are several issues

[LeafShi1]

insertionMark is assigned here but never referenced — the tests access control.InsertionMark directly below. This was inherited from the original, but since these tests are being migrated anyway, it's a good opportunity to remove the unused variable (same applies to the other tests in this file).

[LeafShi1]

The original code had a comment: "changing Application.VisualStyleState sends WM_THEMECHANGED to all controls, which can cause a deadlock if another test fails." — serial execution in UIIntegrationTests mitigates this, but consider adding a brief inline comment explaining why the deadlock concern doesn't apply here (e.g., // Serial execution in UIIntegrationTests prevents cross-test HWND interference).

[LeafShi1]

Other UIIntegrationTests classes typically inherit from ControlTestBase which provides [UseDefaultXunitCulture] and calls EnableVisualStyles. These new test classes are standalone and call Application.EnableVisualStyles() redundantly in each method. Is there a project convention for this? If inheriting is appropriate, it would remove the repetitive calls and ensure these pick up any future base-class infrastructure.