<PackageReference Include="NUnit" Version="3.4.1" />

Contains

public class Contains
Helper class with properties and methods that supply a number of constraints used in Asserts.
using NUnit.Framework.Constraints; namespace NUnit.Framework { public class Contains { public static CollectionContainsConstraint Item(object expected) { return new CollectionContainsConstraint(expected); } public static DictionaryContainsKeyConstraint Key(object expected) { return new DictionaryContainsKeyConstraint(expected); } public static DictionaryContainsValueConstraint Value(object expected) { return new DictionaryContainsValueConstraint(expected); } public static SubstringConstraint Substring(string expected) { return new SubstringConstraint(expected); } } }