From 0aef88d2a3b66620c1d70694bc3d124f2096d323 Mon Sep 17 00:00:00 2001
From: Dag Brattli <dag@brattli.net>
Date: Thu, 28 May 2026 21:38:03 +0200
Subject: [PATCH 1/9] chore: upgrade xunit from v2 to v3

Replace the deprecated xunit v2 (`XUnit` 2.9.3) package with `xunit.v3`
3.2.2 in the Beam, Php, Python and Rust test projects.

v3 test projects are self-executing, so each project now sets
`OutputType=Exe` (added to Rust and Php; Python and Beam already had it)
and the .NET-side `[<EntryPoint>]` is dropped in favour of the runner
entry point generated by xunit.v3:

- Rust `main.fs` is also transpiled to Rust's `fn main`, so its entry
  point is guarded with `#if FABLE_COMPILER` rather than removed.
- Python/Beam/Php had the entry point only in the .NET (`#else`) branch
  of `Main.fs`, which is removed.

`xunit.runner.visualstudio` 3.1.5 is already v3-compatible, so
`dotnet test` continues to work. Test sources need no changes:
`Xunit.FactAttribute`, `Assert.Equal` and `Assert.NotEqual` are
unchanged in v3.

Verified with `dotnet test -c Release`: Rust (2449), Python (2266) and
Beam (2439) pass. The Php project has pre-existing compile errors on
.NET unrelated to xunit and is not run by the build system.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 tests/Beam/Fable.Tests.Beam.fsproj     | 2 +-
 tests/Beam/Main.fs                     | 4 +++-
 tests/Php/Fable.Tests.Php.fsproj       | 2 +-
 tests/Php/Main.fs                      | 4 +++-
 tests/Python/Fable.Tests.Python.fsproj | 2 +-
 tests/Python/Main.fs                   | 4 +++-
 tests/Rust/Fable.Tests.Rust.fsproj     | 3 ++-
 tests/Rust/tests/src/lib.fs            | 6 +++++-
 8 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/tests/Beam/Fable.Tests.Beam.fsproj b/tests/Beam/Fable.Tests.Beam.fsproj
index 54bd8eb912..e79318100e 100644
--- a/tests/Beam/Fable.Tests.Beam.fsproj
+++ b/tests/Beam/Fable.Tests.Beam.fsproj
@@ -10,7 +10,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.7.0" />
-    <PackageReference Include="XUnit" Version="2.9.3" />
+    <PackageReference Include="xunit.v3" Version="3.2.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
diff --git a/tests/Beam/Main.fs b/tests/Beam/Main.fs
index b00af3eaac..7cfe91c15e 100644
--- a/tests/Beam/Main.fs
+++ b/tests/Beam/Main.fs
@@ -2,5 +2,7 @@
 module Program
 ()
 #else
-module Program = let [<EntryPoint>] main _ = 0
+module Program
+// On .NET, xunit.v3 generates the test runner entry point automatically.
+()
 #endif
diff --git a/tests/Php/Fable.Tests.Php.fsproj b/tests/Php/Fable.Tests.Php.fsproj
index 509b2813e4..ec49f9e604 100644
--- a/tests/Php/Fable.Tests.Php.fsproj
+++ b/tests/Php/Fable.Tests.Php.fsproj
@@ -9,7 +9,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.7.0" />
-    <PackageReference Include="XUnit" Version="2.9.3" />
+    <PackageReference Include="xunit.v3" Version="3.2.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
diff --git a/tests/Php/Main.fs b/tests/Php/Main.fs
index ae5f6f6959..d54c0fa690 100644
--- a/tests/Php/Main.fs
+++ b/tests/Php/Main.fs
@@ -2,5 +2,7 @@
 module Program
 ()
 #else
-module Program = let [<EntryPoint>] main _ = 0
+module Program
+// On .NET, xunit.v3 generates the test runner entry point automatically.
+()
 #endif
\ No newline at end of file
diff --git a/tests/Python/Fable.Tests.Python.fsproj b/tests/Python/Fable.Tests.Python.fsproj
index 24ef0fbcf9..79f2f1dc52 100644
--- a/tests/Python/Fable.Tests.Python.fsproj
+++ b/tests/Python/Fable.Tests.Python.fsproj
@@ -10,7 +10,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.10.1" />
-    <PackageReference Include="XUnit" Version="2.9.3" />
+    <PackageReference Include="xunit.v3" Version="3.2.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="4.0.0">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
diff --git a/tests/Python/Main.fs b/tests/Python/Main.fs
index ae5f6f6959..d54c0fa690 100644
--- a/tests/Python/Main.fs
+++ b/tests/Python/Main.fs
@@ -2,5 +2,7 @@
 module Program
 ()
 #else
-module Program = let [<EntryPoint>] main _ = 0
+module Program
+// On .NET, xunit.v3 generates the test runner entry point automatically.
+()
 #endif
\ No newline at end of file
diff --git a/tests/Rust/Fable.Tests.Rust.fsproj b/tests/Rust/Fable.Tests.Rust.fsproj
index 2b9a48b8ba..d266d4d06c 100644
--- a/tests/Rust/Fable.Tests.Rust.fsproj
+++ b/tests/Rust/Fable.Tests.Rust.fsproj
@@ -1,5 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
+    <OutputType>Exe</OutputType>
     <TargetFramework>net10.0</TargetFramework>
     <RollForward>Major</RollForward>
     <IsPackable>false</IsPackable>
@@ -8,7 +9,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.10.1" />
-    <PackageReference Include="XUnit" Version="2.9.3" />
+    <PackageReference Include="xunit.v3" Version="3.2.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="4.0.0">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
diff --git a/tests/Rust/tests/src/lib.fs b/tests/Rust/tests/src/lib.fs
index e448cd8f1f..f9b2027a20 100644
--- a/tests/Rust/tests/src/lib.fs
+++ b/tests/Rust/tests/src/lib.fs
@@ -6,6 +6,10 @@ let _imports() =
     importAll "./ExtInteropTests.rs"
     ()
 
-// Comment the main func when no longer needed (after migrating to xunit v3)
+// [<OuterAttr("cfg", [|"not(feature = \"no_std\")"|])>]
+#if FABLE_COMPILER
+// On .NET, xunit.v3 generates the test runner entry point; only emit our own
+// entry point when transpiling (Rust needs a `fn main`).
 [<EntryPoint>]
 let main _args = 0
+#endif

From 26e15fce01347d3a7da42ae72f03b93fca6de9bc Mon Sep 17 00:00:00 2001
From: Dag Brattli <dag@brattli.net>
Date: Thu, 28 May 2026 22:06:17 +0200
Subject: [PATCH 2/9] chore: stop xunit.v3 attaching runner sources to the
 Fable build

CI revealed that the Fable transpilation of the Rust tests failed with
FS0433 ("EntryPointAttribute must be the last declaration in the last
file"). When Fable cracks a project it defines FABLE_COMPILER and runs
the CoreCompile target, which triggers xunit.v3's _XunitAttachSourceFiles
target. That appends a generated entry point and the built-in runner
reporters after the project's own source files. For Rust this collides
with the `[<EntryPoint>]` in tests/src/main.fs (and those sources also
reference runtime types Fable cannot transpile).

Disable both attached source files for the Fable build only, keyed off
the FABLE_COMPILER MSBuild property that Fable's MSBuildCrackerResolver
passes (`/p:FABLE_COMPILER=True`). On .NET the properties keep their
defaults, so xunit.v3 still generates the test runner entry point.

Verified `dotnet test -c Release` (Rust 2449 passing) and the Fable
transpile (Rust/Python/Beam) all succeed with no xunit sources leaking
into the transpiled output.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 tests/Beam/Fable.Tests.Beam.fsproj     | 7 +++++++
 tests/Php/Fable.Tests.Php.fsproj       | 7 +++++++
 tests/Python/Fable.Tests.Python.fsproj | 7 +++++++
 tests/Rust/Fable.Tests.Rust.fsproj     | 8 ++++++++
 tests/Rust/tests/src/lib.fs            | 4 ++--
 5 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/tests/Beam/Fable.Tests.Beam.fsproj b/tests/Beam/Fable.Tests.Beam.fsproj
index e79318100e..aca94f1a8e 100644
--- a/tests/Beam/Fable.Tests.Beam.fsproj
+++ b/tests/Beam/Fable.Tests.Beam.fsproj
@@ -1,6 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
+    <!-- When Fable cracks the project it defines FABLE_COMPILER and runs CoreCompile,
+         which makes xunit.v3 attach its generated entry point and runner-reporter
+         source files. Those reference .NET runtime types and are irrelevant to the
+         transpiled output, so disable them for the Fable build only; on .NET xunit
+         still generates the test runner entry point. -->
+    <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
+    <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <TargetFramework>net10.0</TargetFramework>
     <RollForward>Major</RollForward>
     <IsPackable>false</IsPackable>
diff --git a/tests/Php/Fable.Tests.Php.fsproj b/tests/Php/Fable.Tests.Php.fsproj
index ec49f9e604..19cad33349 100644
--- a/tests/Php/Fable.Tests.Php.fsproj
+++ b/tests/Php/Fable.Tests.Php.fsproj
@@ -1,6 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
+    <!-- When Fable cracks the project it defines FABLE_COMPILER and runs CoreCompile,
+         which makes xunit.v3 attach its generated entry point and runner-reporter
+         source files. Those reference .NET runtime types and are irrelevant to the
+         transpiled output, so disable them for the Fable build only; on .NET xunit
+         still generates the test runner entry point. -->
+    <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
+    <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <TargetFramework>net10.0</TargetFramework>
     <RollForward>Major</RollForward>
     <IsPackable>false</IsPackable>
diff --git a/tests/Python/Fable.Tests.Python.fsproj b/tests/Python/Fable.Tests.Python.fsproj
index 79f2f1dc52..f17b993fb0 100644
--- a/tests/Python/Fable.Tests.Python.fsproj
+++ b/tests/Python/Fable.Tests.Python.fsproj
@@ -1,6 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
+    <!-- When Fable cracks the project it defines FABLE_COMPILER and runs CoreCompile,
+         which makes xunit.v3 attach its generated entry point and runner-reporter
+         source files. Those reference .NET runtime types and are irrelevant to the
+         transpiled output, so disable them for the Fable build only; on .NET xunit
+         still generates the test runner entry point. -->
+    <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
+    <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <TargetFramework>net10.0</TargetFramework>
     <RollForward>Major</RollForward>
     <IsPackable>false</IsPackable>
diff --git a/tests/Rust/Fable.Tests.Rust.fsproj b/tests/Rust/Fable.Tests.Rust.fsproj
index d266d4d06c..867eb0d4b9 100644
--- a/tests/Rust/Fable.Tests.Rust.fsproj
+++ b/tests/Rust/Fable.Tests.Rust.fsproj
@@ -1,6 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
+    <!-- When Fable cracks the project it defines FABLE_COMPILER and runs CoreCompile,
+         which makes xunit.v3 attach its generated entry point and runner-reporter
+         source files after our own files. That breaks transpilation (F# requires the
+         entry point in tests/src/main.fs to be the last declaration, and those xunit
+         sources reference runtime types Fable can't transpile). Disable them for the
+         Fable build only; on .NET xunit still generates the test runner entry point. -->
+    <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
+    <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <TargetFramework>net10.0</TargetFramework>
     <RollForward>Major</RollForward>
     <IsPackable>false</IsPackable>
diff --git a/tests/Rust/tests/src/lib.fs b/tests/Rust/tests/src/lib.fs
index f9b2027a20..ddaf02e64b 100644
--- a/tests/Rust/tests/src/lib.fs
+++ b/tests/Rust/tests/src/lib.fs
@@ -8,8 +8,8 @@ let _imports() =
 
 // [<OuterAttr("cfg", [|"not(feature = \"no_std\")"|])>]
 #if FABLE_COMPILER
-// On .NET, xunit.v3 generates the test runner entry point; only emit our own
-// entry point when transpiling (Rust needs a `fn main`).
+// Rust needs a `fn main`, so emit the entry point when transpiling. On .NET,
+// xunit.v3 generates the test runner entry point instead (see the .fsproj).
 [<EntryPoint>]
 let main _args = 0
 #endif

From 782e103a0e3c2da526915a7a514d9804bcbdee78 Mon Sep 17 00:00:00 2001
From: Dag Brattli <dag@brattli.net>
Date: Thu, 28 May 2026 23:01:22 +0200
Subject: [PATCH 3/9] chore: run xunit serially in Python tests to avoid
 Windows flake

Several MailboxProcessor/async tests assert from inside a fire-and-forget
`Async.StartImmediate`, whose continuation can run after its test
collection has been torn down. xunit.v3 reports such background-thread
exceptions as catastrophic failures and exits non-zero (xunit v2 silently
ignored them). With parallel test collections this surfaces on Windows as
"Catastrophic failure: Assert.Equal() ... Expected 42, Actual 0".

Add tests/Python/xunit.runner.json disabling test-collection
parallelization so each collection fully drains before the next runs.
This is the only xunit suite that runs on Windows in CI (Rust/Beam/Php
.NET tests run on Linux only; the JS suite uses Expecto).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 tests/Python/Fable.Tests.Python.fsproj | 7 +++++++
 tests/Python/xunit.runner.json         | 5 +++++
 2 files changed, 12 insertions(+)
 create mode 100644 tests/Python/xunit.runner.json

diff --git a/tests/Python/Fable.Tests.Python.fsproj b/tests/Python/Fable.Tests.Python.fsproj
index f17b993fb0..e08e7b9d3a 100644
--- a/tests/Python/Fable.Tests.Python.fsproj
+++ b/tests/Python/Fable.Tests.Python.fsproj
@@ -29,6 +29,13 @@
   <ItemGroup>
     <ProjectReference Include="../../src/Fable.Core/Fable.Core.fsproj" />
   </ItemGroup>
+  <ItemGroup>
+    <!-- Run xunit serially: several MailboxProcessor/async tests assert from a
+         fire-and-forget `Async.StartImmediate`, whose continuation can run after
+         its test collection is torn down. xunit.v3 reports such background-thread
+         exceptions as catastrophic (v2 ignored them), which fails on Windows. -->
+    <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
   <ItemGroup>
     <Compile Include="../Js/Main/Globs/*.fs" />
     <Compile Include="Util.fs" />
diff --git a/tests/Python/xunit.runner.json b/tests/Python/xunit.runner.json
new file mode 100644
index 0000000000..8641732346
--- /dev/null
+++ b/tests/Python/xunit.runner.json
@@ -0,0 +1,5 @@
+{
+  "$schema": "https://xunit.net/schema/current/xunit.runner.schema.json",
+  "parallelizeTestCollections": false,
+  "maxParallelThreads": 1
+}

From f348f64a374f39e0819fa8c1b21097071e831ac7 Mon Sep 17 00:00:00 2001
From: Dag Brattli <dag@brattli.net>
Date: Thu, 11 Jun 2026 16:13:41 +0200
Subject: [PATCH 4/9] chore(tests): extend serial xunit config to Beam/Php and
 tidy review feedback

- Add xunit.runner.json to Beam and Php: their tests use the same
  fire-and-forget Async.StartImmediate pattern as Python, so they are
  exposed to the same xunit.v3 catastrophic background-exception failures.
- Collapse the now-identical #if FABLE_COMPILER branches in
  Beam/Php/Python Main.fs and add the missing trailing newlines.
- Compress the .fsproj comments explaining the cracking workaround.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 tests/Beam/Fable.Tests.Beam.fsproj     | 14 +++++++++-----
 tests/Beam/Main.fs                     |  8 ++------
 tests/Beam/xunit.runner.json           |  5 +++++
 tests/Php/Fable.Tests.Php.fsproj       | 14 +++++++++-----
 tests/Php/Main.fs                      |  8 ++------
 tests/Php/xunit.runner.json            |  5 +++++
 tests/Python/Fable.Tests.Python.fsproj | 15 ++++++---------
 tests/Python/Main.fs                   |  8 ++------
 tests/Rust/Fable.Tests.Rust.fsproj     | 10 ++++------
 9 files changed, 44 insertions(+), 43 deletions(-)
 create mode 100644 tests/Beam/xunit.runner.json
 create mode 100644 tests/Php/xunit.runner.json

diff --git a/tests/Beam/Fable.Tests.Beam.fsproj b/tests/Beam/Fable.Tests.Beam.fsproj
index aca94f1a8e..1f3719664a 100644
--- a/tests/Beam/Fable.Tests.Beam.fsproj
+++ b/tests/Beam/Fable.Tests.Beam.fsproj
@@ -1,11 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <!-- When Fable cracks the project it defines FABLE_COMPILER and runs CoreCompile,
-         which makes xunit.v3 attach its generated entry point and runner-reporter
-         source files. Those reference .NET runtime types and are irrelevant to the
-         transpiled output, so disable them for the Fable build only; on .NET xunit
-         still generates the test runner entry point. -->
+    <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would pull in
+         xunit.v3's generated entry point and runner reporters: .NET-only sources that break
+         transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
     <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
     <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <TargetFramework>net10.0</TargetFramework>
@@ -31,6 +29,12 @@
     <ProjectReference Include="../../src/Fable.Core/Fable.Core.fsproj" />
     <ProjectReference Include="MemberNameCollisionLibrary/MemberNameCollisionLibrary.fsproj" />
   </ItemGroup>
+  <ItemGroup>
+    <!-- Run xunit serially: some MailboxProcessor/async tests assert from fire-and-forget
+         `Async.StartImmediate` continuations that can outlive their test collection, and
+         xunit.v3 reports such background exceptions as catastrophic (v2 ignored them). -->
+    <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
   <ItemGroup>
     <Compile Include="Misc/Aether.fs" />
     <Compile Include="Misc/Imports.fs" />
diff --git a/tests/Beam/Main.fs b/tests/Beam/Main.fs
index 7cfe91c15e..34ec007612 100644
--- a/tests/Beam/Main.fs
+++ b/tests/Beam/Main.fs
@@ -1,8 +1,4 @@
-#if FABLE_COMPILER
 module Program
+// No entry point: Fable does not need one here, and on .NET xunit.v3
+// generates the test runner entry point.
 ()
-#else
-module Program
-// On .NET, xunit.v3 generates the test runner entry point automatically.
-()
-#endif
diff --git a/tests/Beam/xunit.runner.json b/tests/Beam/xunit.runner.json
new file mode 100644
index 0000000000..8641732346
--- /dev/null
+++ b/tests/Beam/xunit.runner.json
@@ -0,0 +1,5 @@
+{
+  "$schema": "https://xunit.net/schema/current/xunit.runner.schema.json",
+  "parallelizeTestCollections": false,
+  "maxParallelThreads": 1
+}
diff --git a/tests/Php/Fable.Tests.Php.fsproj b/tests/Php/Fable.Tests.Php.fsproj
index 19cad33349..ac82791e96 100644
--- a/tests/Php/Fable.Tests.Php.fsproj
+++ b/tests/Php/Fable.Tests.Php.fsproj
@@ -1,11 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <!-- When Fable cracks the project it defines FABLE_COMPILER and runs CoreCompile,
-         which makes xunit.v3 attach its generated entry point and runner-reporter
-         source files. Those reference .NET runtime types and are irrelevant to the
-         transpiled output, so disable them for the Fable build only; on .NET xunit
-         still generates the test runner entry point. -->
+    <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would pull in
+         xunit.v3's generated entry point and runner reporters: .NET-only sources that break
+         transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
     <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
     <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <TargetFramework>net10.0</TargetFramework>
@@ -25,6 +23,12 @@
   <ItemGroup>
     <ProjectReference Include="../../src/Fable.Core/Fable.Core.fsproj" />
   </ItemGroup>
+  <ItemGroup>
+    <!-- Run xunit serially: some async tests assert from fire-and-forget
+         `Async.StartImmediate` continuations that can outlive their test collection, and
+         xunit.v3 reports such background exceptions as catastrophic (v2 ignored them). -->
+    <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
   <ItemGroup>
     <Compile Include="Util.fs" />
     <Compile Include="TestSeq.fs" />
diff --git a/tests/Php/Main.fs b/tests/Php/Main.fs
index d54c0fa690..34ec007612 100644
--- a/tests/Php/Main.fs
+++ b/tests/Php/Main.fs
@@ -1,8 +1,4 @@
-#if FABLE_COMPILER
 module Program
+// No entry point: Fable does not need one here, and on .NET xunit.v3
+// generates the test runner entry point.
 ()
-#else
-module Program
-// On .NET, xunit.v3 generates the test runner entry point automatically.
-()
-#endif
\ No newline at end of file
diff --git a/tests/Php/xunit.runner.json b/tests/Php/xunit.runner.json
new file mode 100644
index 0000000000..8641732346
--- /dev/null
+++ b/tests/Php/xunit.runner.json
@@ -0,0 +1,5 @@
+{
+  "$schema": "https://xunit.net/schema/current/xunit.runner.schema.json",
+  "parallelizeTestCollections": false,
+  "maxParallelThreads": 1
+}
diff --git a/tests/Python/Fable.Tests.Python.fsproj b/tests/Python/Fable.Tests.Python.fsproj
index e08e7b9d3a..a1c78472d9 100644
--- a/tests/Python/Fable.Tests.Python.fsproj
+++ b/tests/Python/Fable.Tests.Python.fsproj
@@ -1,11 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <!-- When Fable cracks the project it defines FABLE_COMPILER and runs CoreCompile,
-         which makes xunit.v3 attach its generated entry point and runner-reporter
-         source files. Those reference .NET runtime types and are irrelevant to the
-         transpiled output, so disable them for the Fable build only; on .NET xunit
-         still generates the test runner entry point. -->
+    <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would pull in
+         xunit.v3's generated entry point and runner reporters: .NET-only sources that break
+         transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
     <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
     <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <TargetFramework>net10.0</TargetFramework>
@@ -30,10 +28,9 @@
     <ProjectReference Include="../../src/Fable.Core/Fable.Core.fsproj" />
   </ItemGroup>
   <ItemGroup>
-    <!-- Run xunit serially: several MailboxProcessor/async tests assert from a
-         fire-and-forget `Async.StartImmediate`, whose continuation can run after
-         its test collection is torn down. xunit.v3 reports such background-thread
-         exceptions as catastrophic (v2 ignored them), which fails on Windows. -->
+    <!-- Run xunit serially: some MailboxProcessor/async tests assert from fire-and-forget
+         `Async.StartImmediate` continuations that can outlive their test collection, and
+         xunit.v3 reports such background exceptions as catastrophic (v2 ignored them). -->
     <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
   </ItemGroup>
   <ItemGroup>
diff --git a/tests/Python/Main.fs b/tests/Python/Main.fs
index d54c0fa690..34ec007612 100644
--- a/tests/Python/Main.fs
+++ b/tests/Python/Main.fs
@@ -1,8 +1,4 @@
-#if FABLE_COMPILER
 module Program
+// No entry point: Fable does not need one here, and on .NET xunit.v3
+// generates the test runner entry point.
 ()
-#else
-module Program
-// On .NET, xunit.v3 generates the test runner entry point automatically.
-()
-#endif
\ No newline at end of file
diff --git a/tests/Rust/Fable.Tests.Rust.fsproj b/tests/Rust/Fable.Tests.Rust.fsproj
index 867eb0d4b9..ce3e5130a6 100644
--- a/tests/Rust/Fable.Tests.Rust.fsproj
+++ b/tests/Rust/Fable.Tests.Rust.fsproj
@@ -1,12 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <!-- When Fable cracks the project it defines FABLE_COMPILER and runs CoreCompile,
-         which makes xunit.v3 attach its generated entry point and runner-reporter
-         source files after our own files. That breaks transpilation (F# requires the
-         entry point in tests/src/main.fs to be the last declaration, and those xunit
-         sources reference runtime types Fable can't transpile). Disable them for the
-         Fable build only; on .NET xunit still generates the test runner entry point. -->
+    <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would append
+         xunit.v3's generated entry point and runner reporters after tests/src/main.fs, breaking
+         transpilation (the entry point must be the last declaration, and those sources are
+         .NET-only). Disable them for the Fable build; the real .NET build keeps them. -->
     <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
     <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <TargetFramework>net10.0</TargetFramework>

From adcdaf310c3ff511a714f2d1da7be8f9c962e2b8 Mon Sep 17 00:00:00 2001
From: Dag Brattli <dag@brattli.net>
Date: Sun, 11 Oct 2026 19:03:36 +0200
Subject: [PATCH 5/9] chore(tests): upgrade xunit v3 to 4.0.2

---
 tests/Beam/Fable.Tests.Beam.fsproj     | 10 ++++++----
 tests/Php/Fable.Tests.Php.fsproj       | 10 ++++++----
 tests/Python/Fable.Tests.Python.fsproj | 10 ++++++----
 tests/Rust/Fable.Tests.Rust.fsproj     | 12 +++++++-----
 4 files changed, 25 insertions(+), 17 deletions(-)

diff --git a/tests/Beam/Fable.Tests.Beam.fsproj b/tests/Beam/Fable.Tests.Beam.fsproj
index 1f3719664a..a608052c22 100644
--- a/tests/Beam/Fable.Tests.Beam.fsproj
+++ b/tests/Beam/Fable.Tests.Beam.fsproj
@@ -2,10 +2,11 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would pull in
-         xunit.v3's generated entry point and runner reporters: .NET-only sources that break
-         transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
+         xunit.v3's generated entry point, runner reporters, and result writers: .NET-only sources
+         that break transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
     <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
     <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
+    <XunitRegisterBuiltInResultWriters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInResultWriters>
     <TargetFramework>net10.0</TargetFramework>
     <RollForward>Major</RollForward>
     <IsPackable>false</IsPackable>
@@ -15,8 +16,9 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.7.0" />
-    <PackageReference Include="xunit.v3" Version="3.2.2" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
+    <!-- Keep the existing VSTest-based dotnet test commands on .NET 10. -->
+    <PackageReference Include="xunit.v3.mtp-off" Version="4.0.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="4.0.1">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
diff --git a/tests/Php/Fable.Tests.Php.fsproj b/tests/Php/Fable.Tests.Php.fsproj
index ac82791e96..60a57811db 100644
--- a/tests/Php/Fable.Tests.Php.fsproj
+++ b/tests/Php/Fable.Tests.Php.fsproj
@@ -2,10 +2,11 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would pull in
-         xunit.v3's generated entry point and runner reporters: .NET-only sources that break
-         transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
+         xunit.v3's generated entry point, runner reporters, and result writers: .NET-only sources
+         that break transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
     <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
     <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
+    <XunitRegisterBuiltInResultWriters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInResultWriters>
     <TargetFramework>net10.0</TargetFramework>
     <RollForward>Major</RollForward>
     <IsPackable>false</IsPackable>
@@ -14,8 +15,9 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.7.0" />
-    <PackageReference Include="xunit.v3" Version="3.2.2" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
+    <!-- Keep the existing VSTest-based dotnet test commands on .NET 10. -->
+    <PackageReference Include="xunit.v3.mtp-off" Version="4.0.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="4.0.1">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
diff --git a/tests/Python/Fable.Tests.Python.fsproj b/tests/Python/Fable.Tests.Python.fsproj
index a1c78472d9..9bbd125734 100644
--- a/tests/Python/Fable.Tests.Python.fsproj
+++ b/tests/Python/Fable.Tests.Python.fsproj
@@ -2,10 +2,11 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would pull in
-         xunit.v3's generated entry point and runner reporters: .NET-only sources that break
-         transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
+         xunit.v3's generated entry point, runner reporters, and result writers: .NET-only sources
+         that break transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
     <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
     <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
+    <XunitRegisterBuiltInResultWriters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInResultWriters>
     <TargetFramework>net10.0</TargetFramework>
     <RollForward>Major</RollForward>
     <IsPackable>false</IsPackable>
@@ -15,8 +16,9 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.10.1" />
-    <PackageReference Include="xunit.v3" Version="3.2.2" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="4.0.0">
+    <!-- Keep the existing VSTest-based dotnet test commands on .NET 10. -->
+    <PackageReference Include="xunit.v3.mtp-off" Version="4.0.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="4.0.1">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
diff --git a/tests/Rust/Fable.Tests.Rust.fsproj b/tests/Rust/Fable.Tests.Rust.fsproj
index ce3e5130a6..20f4b8a24b 100644
--- a/tests/Rust/Fable.Tests.Rust.fsproj
+++ b/tests/Rust/Fable.Tests.Rust.fsproj
@@ -2,11 +2,12 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would append
-         xunit.v3's generated entry point and runner reporters after tests/src/main.fs, breaking
-         transpilation (the entry point must be the last declaration, and those sources are
-         .NET-only). Disable them for the Fable build; the real .NET build keeps them. -->
+         xunit.v3's generated entry point, runner reporters, and result writers after
+         tests/src/main.fs, breaking transpilation (the entry point must be the last declaration,
+         and those sources are .NET-only). Disable them for the Fable build; the real .NET build keeps them. -->
     <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
     <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
+    <XunitRegisterBuiltInResultWriters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInResultWriters>
     <TargetFramework>net10.0</TargetFramework>
     <RollForward>Major</RollForward>
     <IsPackable>false</IsPackable>
@@ -15,8 +16,9 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.10.1" />
-    <PackageReference Include="xunit.v3" Version="3.2.2" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="4.0.0">
+    <!-- Keep the existing VSTest-based dotnet test commands on .NET 10. -->
+    <PackageReference Include="xunit.v3.mtp-off" Version="4.0.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="4.0.1">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>

From c009e72ffe96646fc6cf95782fadf64eb20e437e Mon Sep 17 00:00:00 2001
From: Dag Brattli <dag@brattli.net>
Date: Sun, 11 Oct 2026 19:12:20 +0200
Subject: [PATCH 6/9] chore(tests): limit xunit serialization to Python

---
 tests/Beam/Fable.Tests.Beam.fsproj     | 6 ------
 tests/Beam/xunit.runner.json           | 5 -----
 tests/Php/Fable.Tests.Php.fsproj       | 6 ------
 tests/Php/xunit.runner.json            | 5 -----
 tests/Python/Fable.Tests.Python.fsproj | 6 +++---
 5 files changed, 3 insertions(+), 25 deletions(-)
 delete mode 100644 tests/Beam/xunit.runner.json
 delete mode 100644 tests/Php/xunit.runner.json

diff --git a/tests/Beam/Fable.Tests.Beam.fsproj b/tests/Beam/Fable.Tests.Beam.fsproj
index a608052c22..c714ed508b 100644
--- a/tests/Beam/Fable.Tests.Beam.fsproj
+++ b/tests/Beam/Fable.Tests.Beam.fsproj
@@ -31,12 +31,6 @@
     <ProjectReference Include="../../src/Fable.Core/Fable.Core.fsproj" />
     <ProjectReference Include="MemberNameCollisionLibrary/MemberNameCollisionLibrary.fsproj" />
   </ItemGroup>
-  <ItemGroup>
-    <!-- Run xunit serially: some MailboxProcessor/async tests assert from fire-and-forget
-         `Async.StartImmediate` continuations that can outlive their test collection, and
-         xunit.v3 reports such background exceptions as catastrophic (v2 ignored them). -->
-    <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
-  </ItemGroup>
   <ItemGroup>
     <Compile Include="Misc/Aether.fs" />
     <Compile Include="Misc/Imports.fs" />
diff --git a/tests/Beam/xunit.runner.json b/tests/Beam/xunit.runner.json
deleted file mode 100644
index 8641732346..0000000000
--- a/tests/Beam/xunit.runner.json
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "$schema": "https://xunit.net/schema/current/xunit.runner.schema.json",
-  "parallelizeTestCollections": false,
-  "maxParallelThreads": 1
-}
diff --git a/tests/Php/Fable.Tests.Php.fsproj b/tests/Php/Fable.Tests.Php.fsproj
index 60a57811db..3a4c662693 100644
--- a/tests/Php/Fable.Tests.Php.fsproj
+++ b/tests/Php/Fable.Tests.Php.fsproj
@@ -25,12 +25,6 @@
   <ItemGroup>
     <ProjectReference Include="../../src/Fable.Core/Fable.Core.fsproj" />
   </ItemGroup>
-  <ItemGroup>
-    <!-- Run xunit serially: some async tests assert from fire-and-forget
-         `Async.StartImmediate` continuations that can outlive their test collection, and
-         xunit.v3 reports such background exceptions as catastrophic (v2 ignored them). -->
-    <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
-  </ItemGroup>
   <ItemGroup>
     <Compile Include="Util.fs" />
     <Compile Include="TestSeq.fs" />
diff --git a/tests/Php/xunit.runner.json b/tests/Php/xunit.runner.json
deleted file mode 100644
index 8641732346..0000000000
--- a/tests/Php/xunit.runner.json
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "$schema": "https://xunit.net/schema/current/xunit.runner.schema.json",
-  "parallelizeTestCollections": false,
-  "maxParallelThreads": 1
-}
diff --git a/tests/Python/Fable.Tests.Python.fsproj b/tests/Python/Fable.Tests.Python.fsproj
index 9bbd125734..6f6a8f112a 100644
--- a/tests/Python/Fable.Tests.Python.fsproj
+++ b/tests/Python/Fable.Tests.Python.fsproj
@@ -30,9 +30,9 @@
     <ProjectReference Include="../../src/Fable.Core/Fable.Core.fsproj" />
   </ItemGroup>
   <ItemGroup>
-    <!-- Run xunit serially: some MailboxProcessor/async tests assert from fire-and-forget
-         `Async.StartImmediate` continuations that can outlive their test collection, and
-         xunit.v3 reports such background exceptions as catastrophic (v2 ignored them). -->
+    <!-- Temporary workaround for the Windows failure observed after the xunit.v3 upgrade.
+         Serialization does not await detached Async.StartImmediate workflows.
+         TODO: Remove after .NET async tests await completion and pass with parallel collections on Windows. -->
     <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
   </ItemGroup>
   <ItemGroup>

From e88ac2ddd82bf406275779998682f7c05578586e Mon Sep 17 00:00:00 2001
From: Dag Brattli <dag@brattli.net>
Date: Sun, 11 Oct 2026 19:28:02 +0200
Subject: [PATCH 7/9] chore(tests): remove empty entry files and restore Beam
 CI workaround

---
 tests/Beam/Fable.Tests.Beam.fsproj     | 9 +++++----
 tests/Beam/Main.fs                     | 4 ----
 tests/Beam/xunit.runner.json           | 5 +++++
 tests/Php/Fable.Tests.Php.fsproj       | 5 +----
 tests/Php/Main.fs                      | 4 ----
 tests/Python/Fable.Tests.Python.fsproj | 8 ++------
 tests/Rust/Fable.Tests.Rust.fsproj     | 5 +----
 7 files changed, 14 insertions(+), 26 deletions(-)
 delete mode 100644 tests/Beam/Main.fs
 create mode 100644 tests/Beam/xunit.runner.json
 delete mode 100644 tests/Php/Main.fs

diff --git a/tests/Beam/Fable.Tests.Beam.fsproj b/tests/Beam/Fable.Tests.Beam.fsproj
index c714ed508b..f310f1716d 100644
--- a/tests/Beam/Fable.Tests.Beam.fsproj
+++ b/tests/Beam/Fable.Tests.Beam.fsproj
@@ -1,9 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would pull in
-         xunit.v3's generated entry point, runner reporters, and result writers: .NET-only sources
-         that break transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
+    <!-- Exclude .NET-only xUnit runner sources during Fable project cracking. -->
     <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
     <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <XunitRegisterBuiltInResultWriters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInResultWriters>
@@ -31,6 +29,10 @@
     <ProjectReference Include="../../src/Fable.Core/Fable.Core.fsproj" />
     <ProjectReference Include="MemberNameCollisionLibrary/MemberNameCollisionLibrary.fsproj" />
   </ItemGroup>
+  <ItemGroup>
+    <!-- Temporary CI workaround for detached async assertions; remove once .NET tests await completion. -->
+    <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
   <ItemGroup>
     <Compile Include="Misc/Aether.fs" />
     <Compile Include="Misc/Imports.fs" />
@@ -111,6 +113,5 @@
     <Compile Include="ModuleMutableTwoTests.fs" />
     <Compile Include="ModuleNamingTests.fs" />
     <Compile Include="MemberNamingTests.fs" />
-    <Compile Include="Main.fs" />
   </ItemGroup>
 </Project>
diff --git a/tests/Beam/Main.fs b/tests/Beam/Main.fs
deleted file mode 100644
index 34ec007612..0000000000
--- a/tests/Beam/Main.fs
+++ /dev/null
@@ -1,4 +0,0 @@
-module Program
-// No entry point: Fable does not need one here, and on .NET xunit.v3
-// generates the test runner entry point.
-()
diff --git a/tests/Beam/xunit.runner.json b/tests/Beam/xunit.runner.json
new file mode 100644
index 0000000000..8641732346
--- /dev/null
+++ b/tests/Beam/xunit.runner.json
@@ -0,0 +1,5 @@
+{
+  "$schema": "https://xunit.net/schema/current/xunit.runner.schema.json",
+  "parallelizeTestCollections": false,
+  "maxParallelThreads": 1
+}
diff --git a/tests/Php/Fable.Tests.Php.fsproj b/tests/Php/Fable.Tests.Php.fsproj
index 3a4c662693..b670ce39b8 100644
--- a/tests/Php/Fable.Tests.Php.fsproj
+++ b/tests/Php/Fable.Tests.Php.fsproj
@@ -1,9 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would pull in
-         xunit.v3's generated entry point, runner reporters, and result writers: .NET-only sources
-         that break transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
+    <!-- Exclude .NET-only xUnit runner sources during Fable project cracking. -->
     <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
     <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <XunitRegisterBuiltInResultWriters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInResultWriters>
@@ -38,7 +36,6 @@
     <Compile Include="TestUnionType.fs" />
     <Compile Include="TestLoops.fs" />
     <Compile Include="TestAsync.fs" />
-    <Compile Include="Main.fs" />
 
   </ItemGroup>
 </Project>
diff --git a/tests/Php/Main.fs b/tests/Php/Main.fs
deleted file mode 100644
index 34ec007612..0000000000
--- a/tests/Php/Main.fs
+++ /dev/null
@@ -1,4 +0,0 @@
-module Program
-// No entry point: Fable does not need one here, and on .NET xunit.v3
-// generates the test runner entry point.
-()
diff --git a/tests/Python/Fable.Tests.Python.fsproj b/tests/Python/Fable.Tests.Python.fsproj
index 6f6a8f112a..52232d33ca 100644
--- a/tests/Python/Fable.Tests.Python.fsproj
+++ b/tests/Python/Fable.Tests.Python.fsproj
@@ -1,9 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would pull in
-         xunit.v3's generated entry point, runner reporters, and result writers: .NET-only sources
-         that break transpilation. Disable them for the Fable build; the real .NET build keeps them. -->
+    <!-- Exclude .NET-only xUnit runner sources during Fable project cracking. -->
     <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
     <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <XunitRegisterBuiltInResultWriters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInResultWriters>
@@ -30,9 +28,7 @@
     <ProjectReference Include="../../src/Fable.Core/Fable.Core.fsproj" />
   </ItemGroup>
   <ItemGroup>
-    <!-- Temporary workaround for the Windows failure observed after the xunit.v3 upgrade.
-         Serialization does not await detached Async.StartImmediate workflows.
-         TODO: Remove after .NET async tests await completion and pass with parallel collections on Windows. -->
+    <!-- Temporary Windows CI workaround; remove once .NET async tests await completion. -->
     <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
   </ItemGroup>
   <ItemGroup>
diff --git a/tests/Rust/Fable.Tests.Rust.fsproj b/tests/Rust/Fable.Tests.Rust.fsproj
index 20f4b8a24b..dfd8096cf8 100644
--- a/tests/Rust/Fable.Tests.Rust.fsproj
+++ b/tests/Rust/Fable.Tests.Rust.fsproj
@@ -1,10 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <!-- Fable's project cracking runs CoreCompile with FABLE_COMPILER set, which would append
-         xunit.v3's generated entry point, runner reporters, and result writers after
-         tests/src/main.fs, breaking transpilation (the entry point must be the last declaration,
-         and those sources are .NET-only). Disable them for the Fable build; the real .NET build keeps them. -->
+    <!-- Exclude .NET-only xUnit runner sources during Fable project cracking. -->
     <XunitAutoGeneratedEntryPoint Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitAutoGeneratedEntryPoint>
     <XunitRegisterBuiltInRunnerReporters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInRunnerReporters>
     <XunitRegisterBuiltInResultWriters Condition="'$(FABLE_COMPILER)' == 'True'">false</XunitRegisterBuiltInResultWriters>

From 7f43878d2c8cb41f85a73795af186e8287fcfb63 Mon Sep 17 00:00:00 2001
From: Dag Brattli <dag@brattli.net>
Date: Sun, 11 Oct 2026 19:40:16 +0200
Subject: [PATCH 8/9] chore(tests): remove empty Python entry file

---
 tests/Python/Fable.Tests.Python.fsproj | 1 -
 tests/Python/Main.fs                   | 4 ----
 2 files changed, 5 deletions(-)
 delete mode 100644 tests/Python/Main.fs

diff --git a/tests/Python/Fable.Tests.Python.fsproj b/tests/Python/Fable.Tests.Python.fsproj
index 52232d33ca..92bfcf5106 100644
--- a/tests/Python/Fable.Tests.Python.fsproj
+++ b/tests/Python/Fable.Tests.Python.fsproj
@@ -97,6 +97,5 @@
     <Compile Include="TestNonRegression.fs" />
     <Compile Include="TestQuotation.fs" />
     <Compile Include="TestInlineIfLambda.fs" />
-    <Compile Include="Main.fs" />
   </ItemGroup>
 </Project>
diff --git a/tests/Python/Main.fs b/tests/Python/Main.fs
deleted file mode 100644
index 34ec007612..0000000000
--- a/tests/Python/Main.fs
+++ /dev/null
@@ -1,4 +0,0 @@
-module Program
-// No entry point: Fable does not need one here, and on .NET xunit.v3
-// generates the test runner entry point.
-()

From a47b83e8d0ebc1817fbd1b08b2e4255f0122a524 Mon Sep 17 00:00:00 2001
From: Dag Brattli <dag@brattli.net>
Date: Mon, 12 Oct 2026 08:18:32 +0200
Subject: [PATCH 9/9] fix(rust): retain test harness without an application
 entry point

---
 src/Fable.Transforms/Rust/Fable2Rust.fs | 7 +++++--
 tests/Rust/tests/src/lib.fs             | 8 --------
 2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/src/Fable.Transforms/Rust/Fable2Rust.fs b/src/Fable.Transforms/Rust/Fable2Rust.fs
index 6c0b7943cf..f12cb78d84 100644
--- a/src/Fable.Transforms/Rust/Fable2Rust.fs
+++ b/src/Fable.Transforms/Rust/Fable2Rust.fs
@@ -6480,12 +6480,16 @@ module Compiler =
                 ModuleDepth = 0
             }
 
+        let entryPointItems = file.Declarations |> getEntryPointItems com ctx
+
         let topAttrs =
             [
                 if isLastFileInProject com then
                     // adds "no_std" to crate if feature is enabled
                     mkInnerAttr "cfg_attr" [ "feature = \"no_std\""; "no_std" ]
-                    mkInnerAttr "cfg_attr" [ "feature = \"no_std\""; "no_main" ]
+                    // Libraries retain Cargo's test-harness entry point.
+                    if not (List.isEmpty entryPointItems) then
+                        mkInnerAttr "cfg_attr" [ "feature = \"no_std\""; "no_main" ]
 
                     // TODO: make some of those conditional on compiler options
                     mkInnerAttr "allow" [ "dead_code" ]
@@ -6507,7 +6511,6 @@ module Compiler =
             // mkInnerAttr "feature" ["destructuring_assignment"]
             ]
 
-        let entryPointItems = file.Declarations |> getEntryPointItems com ctx
         let importItems = com.GetAllImports(ctx) |> transformImports com ctx
         let declItems = file.Declarations |> transformDeclarations com ctx
         let modItems = getModuleItems com ctx // global module imports
diff --git a/tests/Rust/tests/src/lib.fs b/tests/Rust/tests/src/lib.fs
index ddaf02e64b..dd4a08ea7a 100644
--- a/tests/Rust/tests/src/lib.fs
+++ b/tests/Rust/tests/src/lib.fs
@@ -5,11 +5,3 @@ open Fable.Core.Rust
 let _imports() =
     importAll "./ExtInteropTests.rs"
     ()
-
-// [<OuterAttr("cfg", [|"not(feature = \"no_std\")"|])>]
-#if FABLE_COMPILER
-// Rust needs a `fn main`, so emit the entry point when transpiling. On .NET,
-// xunit.v3 generates the test runner entry point instead (see the .fsproj).
-[<EntryPoint>]
-let main _args = 0
-#endif