[Rafael-SOWNet]

MultithreadingCancel.TestThoseOnlyCancel asserted two times, and each was wrong on some machine:

• A stopping time. It cancelled a task at 750 ms and asserted at about 1,500 ms that the task had ended as cancelled. On ubuntu-latest the task was sometimes still Running. That is the failure in 12 of the last 40 failed C# Test runs, 8 on master. On a desktop a cancelled task stops within 195 ms, under coverlet within 182 ms, and on one shared core within 129 ms.
• A minimum workload. Every row first checked that 30 solves take at least 3 s. On a desktop they take 2.3 s cold, so all 26 rows failed locally, and they will on CI once the library is fast enough there.

Now each task solves until it is cancelled. The test waits for the cancelled tasks to stop, up to a 30 s budget, then waits as long again in case a task that was not meant to be cancelled shows up. Then it asserts:

• the cancelled tasks are Canceled;
• the rest are still Running, which is stronger than "not cancelled".

A solve that starts with its token already cancelled has to throw. If it returns instead, the task ends as RanToCompletion and the assertion fails, so a library that ignores the token fails the test rather than hanging it.

The test still catches what it is for, checked by breaking the library on purpose:

the library, broken	this test	master's test
ignores the token	20 of 26 rows fail, every row that cancels something, all RanToCompletion; the run ends in 76 s
one token shared by every thread	18 fail, Faulted and RanToCompletion; the 8 that pass are the 6 rows that cancel nothing and the 2 one-task rows
notices a cancel a second late	passes, 26 of 26	3 fail on one core, with the CI message Status: Running; unbroken, it passes there, 26 of 26

The second clock is why master's test was run on one core: on all eight, its 30 solves finish inside 3 s and every row fails before anything is cancelled.

The full unit suite passes on this branch, 17,039 tests, and again pinned to four cores under coverlet.

Fixes #2118.

🤖 Generated with Claude Code

https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura