[Test]
public void When_testing_order_of_lists()
{
  var actual = new[] {1, 2, 3, 4};

  actual.Should().BeInAscendingOrder(x => x);
}

System.ArgumentNullException : A member path cannot be null or empty (Parameter 'dottedPath')
   at FluentAssertions.Common.Guard.ThrowIfArgumentIsNullOrEmpty(String str, String paramName, String message)
   at FluentAssertions.Common.MemberPath..ctor(String dottedPath)
   at FluentAssertions.Common.ExpressionExtensions.GetMemberPath[TDeclaringType,TPropertyType](Expression`1 expression)
   at FluentAssertions.Collections.GenericCollectionAssertions`3.IsValidProperty[TSelector](Expression`1 propertyExpression, String because, Object[] becauseArgs)
   at FluentAssertions.Collections.GenericCollectionAssertions`3.BeOrderedBy[TSelector](Expression`1 propertyExpression, IComparer`1 comparer, SortOrder direction, String because, Object[] becauseArgs)
   at FluentAssertions.Collections.GenericCollectionAssertions`3.BeInAscendingOrder[TSelector](Expression`1 propertyExpression, IComparer`1 comparer, String because, Object[] becauseArgs)
   at FluentAssertions.Collections.GenericCollectionAssertions`3.BeInAscendingOrder[TSelector](Expression`1 propertyExpression, String because, Object[] becauseArgs)