Updated version for NSubstitute 4.x of https://www.neovolve.com/2014/10/07/bridging-between-nsubstitute-and-fluentassertions/

Verify.cs

public static class Verify
{
    /// <summary>
    /// Verifies that the fluent assertions in the <paramref name="action" /> are correct.
    /// </summary>
    /// <param name="action">An action with one or more fluent assertions</param>
    public static T That<T>(Action<T> action)
    {
        return ArgumentMatcher.Enqueue(new AssertionMatcher<T>(action));
    }

    private class AssertionMatcher<T> : IArgumentMatcher<T>
    {
        private readonly Action<T> _assertion;

        public AssertionMatcher(Action<T> assertion)
        {
            _assertion = assertion;
        }

        public bool IsSatisfiedBy(T argument)
        {
            using (var scope = new AssertionScope())
            {
                _assertion(argument);

                var failures = scope.Discard().ToList();

                if (failures.Count == 0)
                {
                    return true;
                }

                failures.ForEach(x => Trace.WriteLine(x));

                return false;
            }
        }
    }
}