"Collection was modified; enumeration operation may not execute"

[steingran]

Got this one when tests were running in Github Actions:

[xUnit.net 00:00:02.44] System.InvalidOperationException : Collection was modified; enumeration operation may not execute. [xUnit.net 00:00:02.45] Stack Trace: [xUnit.net 00:00:02.44] MultiLock.Tests.LeadershipExtensionMethodsTests.WhileLeader_ShouldContinueWhileLeader [FAIL] [xUnit.net 00:00:02.45] at System.Collections.Generic.List1.Enumerator.MoveNext()
[xUnit.net 00:00:02.45] at System.Linq.Enumerable.WhereListIterator1.MoveNext() [xUnit.net 00:00:02.45] at System.Linq.Enumerable.<Any>g__WithEnumerator|36_0[TSource](IEnumerable1 source)
[xUnit.net 00:00:02.45] at System.Linq.Enumerable.Any[TSource](IEnumerable1 source) [xUnit.net 00:00:02.46] /_/src/Shouldly/ShouldlyExtensionMethods/ShouldBeEnumerableTestExtensions.cs(72,0): at Shouldly.ShouldBeEnumerableTestExtensions.ShouldAllBe[T](IEnumerable1 actual, Expression1 elementPredicate, String customMessage) [xUnit.net 00:00:02.46] /home/runner/work/MultiLock/MultiLock/tests/MultiLock.Tests/LeadershipExtensionMethodsTests.cs(590,0): at MultiLock.Tests.LeadershipExtensionMethodsTests.WhileLeader_ShouldContinueWhileLeader() [xUnit.net 00:00:02.46] --- End of stack trace from previous location --- warn: MultiLock.ZooKeeper.ZooKeeperLeaderElectionProvider[0] ZooKeeper connection lost warn: MultiLock.ZooKeeper.ZooKeeperLeaderElectionProvider[0] ZooKeeper connection lost Passed MultiLock.Tests.AsyncEnumerableApiTests.GetLeadershipChangesAsync_ShouldEmitLostEvent_WhenLosingLeadership [88 ms] Failed MultiLock.Tests.LeadershipExtensionMethodsTests.WhileLeader_ShouldContinueWhileLeader [89 ms] Error Message: System.InvalidOperationException : Collection was modified; enumeration operation may not execute. Stack Trace: at System.Collections.Generic.List1.Enumerator.MoveNext()
at System.Linq.Enumerable.WhereListIterator1.MoveNext() at System.Linq.Enumerable.<Any>g__WithEnumerator|36_0[TSource](IEnumerable1 source)
at System.Linq.Enumerable.Any[TSource](IEnumerable1 source) at Shouldly.ShouldBeEnumerableTestExtensions.ShouldAllBe[T](IEnumerable1 actual, Expression1 elementPredicate, String customMessage) in /_/src/Shouldly/ShouldlyExtensionMethods/ShouldBeEnumerableTestExtensions.cs:line 72 at MultiLock.Tests.LeadershipExtensionMethodsTests.WhileLeader_ShouldContinueWhileLeader() in /home/runner/work/MultiLock/MultiLock/tests/MultiLock.Tests/LeadershipExtensionMethodsTests.cs:line 590 --- End of stack trace from previous location --- Passed MultiLock.Tests.LeadershipExtensionMethodsTests.Where_ShouldFilterEvents [83 ms] Passed MultiLock.Tests.LeadershipExtensionMethodsTests.TakeUntilLeader_ShouldStopWhenBecomingLeader [90 ms] Passed MultiLock.Tests.LeadershipExtensionMethodsTests.BufferByTime_ShouldGroupEventsByTimeWindow [405 ms] Passed MultiLock.Tests.LeadershipExtensionMethodsTests.OnLeadershipTransition_WithAsyncCallbacks_ShouldExecuteAsyncCallbacks [111 ms] Passed MultiLock.Tests.LeadershipExtensionMethodsTests.ForEachAsync_WithAsyncAction_ShouldExecuteAsyncActionForEachEvent [98 ms] Passed MultiLock.Tests.LeadershipExtensionMethodsTests.Throttle_ShouldLimitEventRate [321 ms] Passed MultiLock.Tests.LeadershipExtensionMethodsTests.ForEachAsync_ShouldExecuteActionForEachEvent [97 ms] warn: MultiLock.ZooKeeper.ZooKeeperLeaderElectionProvider[0] ZooKeeper connection lost [xUnit.net 00:00:03.76] Finished: MultiLock.Tests warn: MultiLock.Redis.RedisLeaderElectionProvider[0] Heartbeat update failed for participant participant-1 in group test-group - not the current leader