Imported Upstream version 3.8.0

Former-commit-id: 6a76a29bd07d86e57c6c8da45c65ed5447d38a61

mcs/tests/gtest-617.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Collections.Generic;
+ 
+class Program
+{
+	static void Main()
+	{
+		foreach (string x in new B ()) {
+		}
+	}
+}
+
+class A
+{
+	public IEnumerator<string> GetEnumerator ()
+	{
+		var s = new List<string>();
+		s.Add("1"); 
+		return s.GetEnumerator();
+	}
+}
+
+class B : A
+{
+	public IEnumerator<int> GetEnumerator (int[] x = null)
+	{
+		throw new NotImplementedException ();
+	}
+}