Fail F# tests whose return value xUnit never executes

[T-Gro]

An F# [<Fact>]/[<Theory>] that is accidentally a partial application — or otherwise returns a value xUnit never runs, an FSharpFunc, a delegate, or a Lazy<_> — executes none of its assertions yet still reports success. A custom test framework now fails such a method at discovery time by swapping it for xUnit's own ExecutionErrorTestCase; only discovery is customized, so parallelism, console capture, and the rest of the runner chain stay stock.

This is expected to turn currently-green tests red where a body silently never ran.

[github-actions]

✅ No release notes required

[T-Gro]

Guard fired on CI (build 1565003): 8 test legs red, 19 FsharpSuiteMigrated_CoreTests methods return FSharpFunc`2 and never ran.

Root cause — two curried helpers drop the trailing sessionIsolation arg, so the call is a partial application xUnit never executes:

let singleTestBuildAndRunVersion folder mode version = singleTestBuildAndRunAuxVersion folder [] mode version           // missing sessionIsolation
let singleTestBuildAndRunAux folder bonusArgs mode    = singleTestBuildAndRunAuxVersion folder bonusArgs mode LangVersion.Latest  // missing sessionIsolation

Dead tests exposed:

• array-FSC_DEBUG-8_0, array-FSC_OPTIMIZED-8_0, array-FSC_OPTIMIZED-preview, array-FSI-8_0
• array-no-dot-FSC_DEBUG, array-no-dot-FSC_OPTIMIZED, array-no-dot-FSI
• auto-widen-minimal, auto-widen-version-FSC_DEBUG-preview, auto-widen-version-FSC_OPTIMIZED-preview
• controlChamenos-FSC_OPTIMIZED, controlChamenos-FSI
• control --tailcalls, controlMailbox --tailcalls
• namespaceAttributes-FSC_DEBUG, namespaceAttributes-FSC_OPTIMIZED
• patterns-FSC_OPTIMIZED
• printf, printf-interpolated

[T-Gro]

@jwosty :
Great work with spotting those initially 👍 .
Doing the "custom xunit analyzer" reveled one more helper not covered. We should have had this ages ago.