Add C-Sharp (C#) syntax highlighting test files

tests/syntax-tests/source/C-Sharp/Stack.cs

@@ -0,0 +1,64 @@
+namespace StackImplementation
+{
+    internal class Stack<T>
+    {
+        private int _top;
+        private const int Capacity = 4;
+        private readonly T[] _stack = new T[Capacity];
+
+        public Stack()
+        {
+            _top = -1;
+        }
+
+        private bool IsEmpty()
+        {
+            return _top < 0;
+        }
+        private bool IsFull()
+        {
+            return _top == Capacity - 1;
+        }
+
+        public void Peek()
+        {
+            System.Console.WriteLine(!IsEmpty() ? $"The topmost element is: {_stack[_top]}" : "The stack is empty.");
+        }
+
+        public T Pop()
+        {
+            return !IsEmpty() ? _stack[_top--] : default;
+        }
+
+        public void Push(T element)
+        {
+            if (!IsFull())
+            {
+                _stack[++_top] = element;
+            }
+            else
+            {
+                System.Console.WriteLine("Cannot push - the stack is full.");
+            }
+        }
+
+        public override string ToString()
+        {
+            if (IsEmpty())
+            {
+                return "The stack is empty.";
+            }
+
+            var depiction = "";
+
+            for (var index = 0; index < _top; index++)
+            {
+                depiction += _stack[index].ToString() + ' ';
+            }
+
+            depiction += _stack[_top].ToString();
+
+            return $"Stack: [{depiction}]";
+        }
+    }
+}