add cow_ptr test

TinySTL/Test/COWPtrTest.cpp

@@ -0,0 +1,24 @@
+#include "COWPtrTest.h"
+
+#include "../String.h"
+
+namespace TinySTL{
+	namespace COWPtrTest{
+		void testCase1(){
+			cow_ptr<string> cp1(new string("hello"));
+			assert(*cp1 == "hello");
+			
+			cp1->append(" world");
+			auto cp2 = cp1;
+			assert(*cp2 == "hello world");
+
+			cow_ptr<string> cp3;
+			cp3 = cp1;
+			assert(*cp3 == "hello world");
+		}
+
+		void testAllCases(){
+			testCase1();
+		}
+	}
+}