<PackageReference Include="NUnit" Version="2.6.7" />

Contains

public class Contains
Helper class with properties and methods that supply a number of constraints used in Asserts.
public Contains()

public static CollectionContainsConstraint Item(object expected)

Returns a new CollectionContainsConstraint checking for the presence of a particular object in the collection.

public static SubstringConstraint Substring(string expected)

Returns a constraint that succeeds if the actual value contains the substring supplied as an argument.