Add tf.scan test cases

test/TensorFlowNET.UnitTest/functional_ops_test/ScanTestCase.cs

@@ -0,0 +1,39 @@
+using System;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using NumSharp;
+using Tensorflow;
+using static Tensorflow.Binding;
+
+namespace TensorFlowNET.UnitTest.functional_ops_test
+{
+    /// <summary>
+    /// https://www.tensorflow.org/api_docs/python/tf/scan
+    /// </summary>
+    [TestClass]
+    public class ScanTestCase
+    {
+        [TestMethod]
+        public void ScanForward()
+        {
+            var fn = new Func<Tensor, Tensor, Tensor>((a, x) => tf.add(a, x));
+            
+            var sess = tf.Session().as_default();
+
+            var input = tf.placeholder(TF_DataType.TF_INT32, new TensorShape(6));
+            var scan = functional_ops.scan(fn, input);
+            sess.run(scan, (input, np.array(1,2,3,4,5,6))).Should().Be(np.array(1,3,6,10,15,21));
+        }
+
+        [TestMethod]
+        public void ScanReverse()
+        {
+            var fn = new Func<Tensor, Tensor, Tensor>((a, x) => tf.add(a, x));
+            
+            var sess = tf.Session().as_default();
+
+            var input = tf.placeholder(TF_DataType.TF_INT32, new TensorShape(6));
+            var scan = functional_ops.scan(fn, input, reverse:true);
+            sess.run(scan, (input, np.array(1,2,3,4,5,6))).Should().Be(np.array(21,20,18,15,11,6));
+        }
+    }
+}