[tests] Port the ModelMustBeProtocol test from monotouch-test to cecil-test. (#19561)

It uses reflection, so it upsets NativeAOT, so just move it to cecil-test instead.

This will make it run faster, and also more predictable (it's supposed to
check all types, but types in monotouch-test may have been linked away).

Ref: https://github.com/dotnet/runtime/issues/95444

tests/cecil-tests/AttributeTest.cs

@@ -583,5 +583,56 @@ namespace Cecil.Tests {
 
 		bool IsAvailabilityAttribute (CustomAttribute attribute) => IsSupportedAttribute (attribute) || attribute.AttributeType.Name == "UnsupportedOSPlatformAttribute";
 		bool IsSupportedAttribute (CustomAttribute attribute) => attribute.AttributeType.Name == "SupportedOSPlatformAttribute";
+
+		[TestCaseSource (typeof (Helper), nameof (Helper.NetPlatformAssemblyDefinitions))]
+		public void ModelMustBeProtocol (AssemblyInfo info)
+		{
+			// Verify that all types with a [Model] attribute must also have a [Protocol] attribute.
+			// Exception: If the type in question has a [Register] attribute with IsWrapper = false, then that's OK.
+			var failures = new HashSet<string> ();
+			var typesWithModelAttribute = 0;
+			var typesWithProtocolAttribute = 0;
+			var assembly = info.Assembly;
+
+			foreach (var type in assembly.EnumerateTypes ()) {
+				if (!type.HasCustomAttributes)
+					continue;
+
+				var attributes = type.CustomAttributes;
+
+				if (!attributes.Any (v => v.AttributeType.Is ("Foundation", "ModelAttribute")))
+					continue;
+				typesWithModelAttribute++;
+
+				if (attributes.Any (v => v.AttributeType.Is ("Foundation", "ProtocolAttribute"))) {
+					typesWithProtocolAttribute++;
+					continue;
+				}
+
+				var registerAttribute = attributes.SingleOrDefault (v => v.AttributeType.Is ("Foundation", "RegisterAttribute"));
+				if (registerAttribute is not null && !GetIsWrapper (registerAttribute))
+					continue;
+
+				failures.Add ($"The type {type.FullName} has a [Model] attribute, but no [Protocol] attribute.");
+			}
+
+			Assert.That (failures, Is.Empty, "Failures");
+			Assert.That (typesWithModelAttribute, Is.GreaterThan (0), "No types with the [Model] attribute?");
+			Assert.That (typesWithProtocolAttribute, Is.GreaterThan (0), "No types with the [Protocol] attribute?");
+
+			static bool GetIsWrapper (CustomAttribute attrib)
+			{
+				// .ctor (string name, bool isWrapper)
+				if (attrib.ConstructorArguments.Count == 2)
+					return (bool) attrib.ConstructorArguments [1].Value;
+
+				// public bool IsWrapper { get; set; }
+				foreach (var field in attrib.Fields) {
+					if (field.Name == "IsWrapper")
+						return (bool) field.Argument.Value;
+				}
+				return false;
+			}
+		}
 	}
 }

tests/monotouch-test/Foundation/ProtocolAttributeTest.cs

@@ -1,52 +0,0 @@
-//
-// Unit tests for ProtocolAttribute (yeah, really!)
-//
-// Authors:
-//	Rolf Bjarne Kvinge <rolf@xamarin.com>
-//
-// Copyright 2013 Xamarin Inc. All rights reserved.
-//
-
-using System;
-using Foundation;
-using ObjCRuntime;
-using NUnit.Framework;
-
-namespace MonoTouchFixtures.Foundation {
-
-	[TestFixture]
-	[Preserve (AllMembers = true)]
-	public class ProtocolAttributeTest {
-
-		[Test]
-		public void ModelMustBeProtocol ()
-		{
-			int count = 0;
-
-			//
-			// Note that [Model], but no [Protocol] is not a universal truth (so it's
-			// not enforced in the generator), but it should be true for monotouch.dll.
-			//
-
-			foreach (var type in typeof (NSObject).Assembly.GetTypes ()) {
-				if (!type.IsSubclassOf (typeof (NSObject)))
-					continue;
-
-				var register = (RegisterAttribute) Attribute.GetCustomAttribute (type, typeof (RegisterAttribute), false);
-				if (register is not null && !register.IsWrapper)
-					continue;
-
-				if (Attribute.GetCustomAttribute (type, typeof (ModelAttribute), false) is null)
-					continue;
-
-				if (Attribute.GetCustomAttribute (type, typeof (ProtocolAttribute), false) is null) {
-					Console.WriteLine ("{0} must have a [Protocol] attribute if it has a [Model] attribute", type.FullName);
-					count++;
-				}
-			}
-
-			if (count > 0)
-				Assert.Fail ("Found {0} types with a [Model] attribute (and no [Register(false)] attribute signalling that they're not wrapper types), but without a [Protocol] attribute.", count);
-		}
-	}
-}