Fix fifoset (2x) (#904)

* Fix fifo set enumerable

* Rename

* Update UT_FifoSet.cs

neo.UnitTests/UT_FifoSet.cs

@@ -0,0 +1,32 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Neo.IO.Caching;
+using System.Linq;
+
+namespace Neo.UnitTests
+{
+    [TestClass]
+    public class UT_FifoSet
+    {
+        [TestMethod]
+        public void FifoSetTest()
+        {
+            var a = UInt256.Zero;
+            var b = new UInt256();
+            var c = new UInt256(new byte[32] {
+                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
+                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
+                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
+                0x01, 0x01
+            });
+
+            var set = new FIFOSet<UInt256>(3);
+
+            Assert.IsTrue(set.Add(a));
+            Assert.IsFalse(set.Add(a));
+            Assert.IsFalse(set.Add(b));
+            Assert.IsTrue(set.Add(c));
+
+            CollectionAssert.AreEqual(set.ToArray(), new UInt256[] { a, c });
+        }
+    }
+}

neo/IO/Caching/FIFOSet.cs

@@ -51,7 +51,7 @@ public void ExceptWith(IEnumerable<UInt256> hashes)
 
         public IEnumerator<T> GetEnumerator()
         {
-            var entries = dictionary.Values.Cast<T>().ToArray();
+            var entries = dictionary.Keys.Cast<T>().ToArray();
             foreach (var entry in entries) yield return entry;
         }