Add test case for explicit interface implementation involving nullable types

ICSharpCode.Decompiler.Tests/TestCases/Pretty/NullableRefTypes.cs

@@ -1,5 +1,6 @@
 #nullable enable
 using System;
+using System.Collections;
 using System.Collections.Generic;
 
 namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
@@ -139,4 +140,48 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			Console.WriteLine(format, num, num2, tuple);
 		}
 	}
+
+	public class T06_ExplicitInterfaceImplementation : IEnumerable<KeyValuePair<string, string?>>, IEnumerable
+	{
+		// TODO: declaring type is not yet rendered with nullability annotations from the base type
+		IEnumerator<KeyValuePair<string, string?>> IEnumerable<KeyValuePair<string, string>>.GetEnumerator()
+		{
+			yield return new KeyValuePair<string, string>("a", "b");
+		}
+
+		IEnumerator IEnumerable.GetEnumerator()
+		{
+			throw new NotImplementedException();
+		}
+	}
+
+	public class T07_ExplicitInterfaceImplementation : IEnumerator<KeyValuePair<string, string?>>, IEnumerator, IDisposable
+	{
+		KeyValuePair<string, string?> IEnumerator<KeyValuePair<string, string>>.Current {
+			get {
+				throw new NotImplementedException();
+			}
+		}
+
+		object IEnumerator.Current {
+			get {
+				throw new NotImplementedException();
+			}
+		}
+
+		void IDisposable.Dispose()
+		{
+			throw new NotImplementedException();
+		}
+
+		bool IEnumerator.MoveNext()
+		{
+			throw new NotImplementedException();
+		}
+
+		void IEnumerator.Reset()
+		{
+			throw new NotImplementedException();
+		}
+	}
 }