<PackageReference Include="NUnit" Version="4.3.2" />

NUnitString

public struct NUnitString
A class to allow postponing the actual formatting of interpolated strings.
using System; using System.Runtime.CompilerServices; namespace NUnit.Framework { [System.Runtime.CompilerServices.NullableContext(2)] [System.Runtime.CompilerServices.Nullable(0)] public readonly struct NUnitString { private readonly string _message; public NUnitString(string message) { _message = message; } public static implicit operator NUnitString(FormattableString formattableMessage) { throw new NotImplementedException(); } public static implicit operator NUnitString(string message) { return new NUnitString(message); } [System.Runtime.CompilerServices.NullableContext(1)] public override string ToString() { return _message ?? string.Empty; } } }