InvalidOperationException in PythonClassType.GetMemberNames in datetime caching test #1678

 Datetime
   Source: LibraryModulesTests.cs line 94
   Duration: 13 sec

  Message: 
    Assert.Fail failed. One not awaited tasks has failed:
    
    System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
       at bool System.Collections.Generic.Dictionary<TKey, TValue>+KeyCollection+Enumerator.MoveNext()
       at void System.Collections.Generic.HashSet<T>.UnionWith(IEnumerable<T> other)
       at new System.Collections.Generic.HashSet<T>(IEnumerable<T> collection, IEqualityComparer<T> comparer)
       at IEnumerable<string> Microsoft.Python.Analysis.Types.PythonClassType.GetMemberNames() in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Types/PythonClassType.cs:line 73
       at IEnumerable<string> Microsoft.Python.Analysis.Types.PythonClassType.GetMemberNames() in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Types/PythonClassType.cs:line 75
       at IEnumerable<string> Microsoft.Python.Analysis.Types.PythonClassType.GetMemberNames() in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Types/PythonClassType.cs:line 75
       at void Microsoft.Python.Analysis.Analyzer.StubMerger.MergeClass(IVariable v, IPythonClassType sourceClass, IPythonType stubType, CancellationToken cancellationToken) in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Analyzer/StubMerger.cs:line 187
       at void Microsoft.Python.Analysis.Analyzer.StubMerger.TryReplaceMember(IVariable v, IPythonType sourceType, IPythonType stubType, CancellationToken cancellationToken) in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Analyzer/StubMerger.cs:line 114
       at void Microsoft.Python.Analysis.Analyzer.StubMerger.TransferTypesFromStub(IDocumentAnalysis stubAnalysis, CancellationToken cancellationToken) in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Analyzer/StubMerger.cs:line 97
       at void Microsoft.Python.Analysis.Analyzer.StubMerger.MergeStub(IDocumentAnalysis stubAnalysis, CancellationToken cancellationToken) in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Analyzer/StubMerger.cs:line 57
       at void Microsoft.Python.Analysis.Analyzer.ModuleWalker.Complete() in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Analyzer/ModuleWalker.cs:line 206
       at IDocumentAnalysis Microsoft.Python.Analysis.Analyzer.PythonAnalyzerSession.DoAnalyzeEntry(IDependencyChainNode<PythonAnalyzerEntry> node, IPythonModule module, PythonAst ast, int version) in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Analyzer/PythonAnalyzerSession.cs:line 358
       at void Microsoft.Python.Analysis.Analyzer.PythonAnalyzerSession.AnalyzeEntry(IDependencyChainNode<PythonAnalyzerEntry> node, PythonAnalyzerEntry entry, IPythonModule module, PythonAst ast, int version) in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Analyzer/PythonAnalyzerSession.cs:line 336
       at void Microsoft.Python.Analysis.Analyzer.PythonAnalyzerSession.Analyze(IDependencyChainNode<PythonAnalyzerEntry> node, AsyncCountdownEvent ace, Stopwatch stopWatch) in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Analyzer/PythonAnalyzerSession.cs:line 256
       at void Microsoft.Python.Analysis.Analyzer.PythonAnalyzerSession.LogException(IPythonModule module, Exception exception) in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Analyzer/PythonAnalyzerSession.cs:line 455
       at void Microsoft.Python.Analysis.Analyzer.PythonAnalyzerSession.Analyze(IDependencyChainNode<PythonAnalyzerEntry> node, AsyncCountdownEvent ace, Stopwatch stopWatch) in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Analyzer/PythonAnalyzerSession.cs:line 265
       at Task Microsoft.Python.Analysis.Analyzer.PythonAnalyzerSession.StartAnalysis(IDependencyChainNode<PythonAnalyzerEntry> node, AsyncCountdownEvent ace, Stopwatch stopWatch)+() => { } in C:/Users/jabaile/python-language-server/src/Analysis/Ast/Impl/Analyzer/PythonAnalyzerSession.cs:line 242
       at void System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, object state)
       at void System.Threading.Tasks.Task.ExecuteWithThreadLocal(ref Task currentTaskSlot, Thread threadPoolThread)
    
    
  Stack Trace: 
    TaskObserver.Summarize() line 150
    TaskObserver.WaitForObservedTask() line 65
    TestEnvironmentImpl.AfterTestRun() line 117
    TestEnvironmentImpl.TestCleanup() line 54
    LibraryModulesTests.Cleanup() line 39

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