Re-enable library tests skipped on Browser (wasm/CoreCLR) for being too slow in the outerloop lane

[radekdoulik]

Background

PR #129436 adds a WebAssembly + CoreCLR libraries-test leg to the scheduled outerloop pipeline, enabling [OuterLoop] and long-running suites (re-enabled from #125495) with extended Helix/xharness timeouts.

A handful of individual tests are still too slow or too resource-heavy to finish within the per-suite xharness timeout (4h) on the single-threaded wasm interpreter, so they were skipped on Browser via [SkipOnPlatform(TestPlatforms.Browser, …)]. This issue tracks those skips so they can be revisited when wasm test execution gets faster (e.g. JIT/AOT for test runs, threading) or the tests are made cheaper.

These skips only affect the new wasm/CoreCLR outerloop lane — desktop and other platforms are unchanged, and these tests never ran on any wasm innerloop lane.

Tests skipped because they are too slow (CPU time) on the wasm interpreter

Suite	Test	Why slow on wasm
System.Linq.Expressions	CompilerTests.CompileDeepTree_NoStackOverflow	compiles a 10,000-deep expression tree
System.Memory	EncodingExtensionsTests.GetBytes_Encoding_ReadOnlySequence_IBufferWriter_LargeMultiSegment	iterates ~3.2bn chars of UTF-16
System.Memory	EncodingExtensionsTests.GetChars_Encoding_ReadOnlySequence_IBufferWriter_LargeMultiSegment	iterates ~6.5bn bytes of UTF-8
System.Text.Json	BitStackTests.BitStackPushPopLarge	pushes/pops up to 67M bits
System.Text.Json	Stream.ReadTests.ReadTypeFromJsonWithLargeIgnoredProperties_OuterLoop	processes 5 GiB of JSON
System.Text.Json	Utf8JsonReaderTests.TestJsonReaderLargestUtf8SegmentSizeOne	O(n²) single-byte segment slicing
System.Text.Json	Utf8JsonReaderTests.TestPartialJsonReaderSlicesMultiSegment	O(n²) multi-segment slicing (one row ≈ 32 min)
System.Text.Json	Utf8JsonReaderTests.TestPartialJsonReaderSlicesSpecialNumbers	O(n²) slicing of special numbers
System.Text.Json	Utf8JsonWriterTests.Writing3MBBase64Bytes	writes a 3 MB base64 payload across every option combo
System.Text.Json	Utf8JsonWriterTests.EscapeCharacters	every writer-option combo (already [OuterLoop] on Mono)
System.Text.Json	Utf8JsonWriterTests.WriteNumbers	every writer-option combo (already [OuterLoop] on Mono)

Tests skipped due to memory exhaustion on the constrained wasm heap (related)

Suite	Test	Why
System.Collections.Immutable	FrozenDictionaryTests.ToFrozenDictionary_WithExtremelyLargeStrings	allocates ~1 GB strings
System.Collections.Immutable	FrozenSetTests.ToFrozenSet_WithExtremelyLargeStrings	allocates ~1 GB strings

Whole [OuterLoop] category skipped for one suite

• System.Linq.Parallel.Tests — the full [OuterLoop] combinatorial matrix expands to ~195k cases on a single-threaded wasm session (~72 MB results file exceeding xharness's 30 MB upload limit, ~1.3 GB heap, tab crash at teardown). PLINQ has no real parallelism on a single thread, so this is dropped on the wasm/CoreCLR lane via WithoutCategories=OuterLoop.

Related — different root cause (a hang, not slowness)

• System.Private.Xml.Linq xNodeBuilder/FunctionalTests.RunTests — also skipped on Browser in [browser][coreclr] Add wasm/CoreCLR libraries tests to outerloop CI #129436, but because the wasm runtime hangs at shutdown after this suite completes (a hang, not slowness). Listed here for completeness; likely warrants its own investigation.

Re-enablement criteria

Revisit each skip when wasm test execution is materially faster (JIT/AOT for test assemblies, multithreaded runtime) or when the individual tests are restructured to be cheaper.
Related: #125495, #129436.

Note

This issue was drafted with the help of GitHub Copilot.

[dotnet-policy-service]

Tagging subscribers to 'arch-wasm': @lewing, @pavelsavara
See info in area-owners.md if you want to be subscribed.