<PackageReference Include="NETStandard.Library" Version="2.0.2" />

System.Diagnostics.Contracts.ContractFailureKind

public enum ContractFailureKind
namespace System.Diagnostics.Contracts { public enum ContractFailureKind { Assert = 4, Assume = 5, Invariant = 3, Postcondition = 1, PostconditionOnException = 2, Precondition = 0 } }