Case Insensitive comparison for collection against multiple options - nunit

Question

I am trying to use NUnit to write an assertion that all the (string) members of a collection are one of a set of possibilities in a case insensitive manner. I thought I had figured it out, but it won't compile.
I thought this syntax would work:
Assert.That(new string[] { "red", "red", "red", "green" },
Is.All.AnyOf(new string[] { "RED", "BLUE", "GREEN" }).IgnoreCase);
However this errors with
'Constraint' does not contain a definition for 'IgnoreCase' and no
extension method 'IgnoreCase' accepting a first argument of
type 'Constraint' could be found (are you missing a using directive or an
assembly reference?)
The simpler test of a single item is one of a set of possibilities in a case insensitive manner works as expected.
Assert.That("red", Is.AnyOf(new string[] { "RED", "BLUE" }).IgnoreCase);
How should I phrase this assertion? Or is it a bug that this does not work?

Answer 1

You are running into the issue because of the order of precedence of the operations. You want the .IgnoreCase modifier to apply to the AnyOfConstraint, but it is being applied to the result of IsAll, which is a base level Constraint that doesn't support that modifier.
Barring changes to NUnit, you need a workaround. The simplest would appear to be
Assert.That(new string[] { "red", "red", "red", "green" },
new AllItemsConstraint(
Is.AnyOf(new string[] { "RED", "BLUE", "GREEN" }).IgnoreCase));
I haven't tried this, so check my syntax, spelling, etc.