Added padding functionality

Test/String__PadLeft.cpp

@@ -0,0 +1,44 @@
+#include <StringTools.h>
+#include "Catch2.h"
+
+// Tests that padding to a length shorter adds no padding 
+TEST_CASE(__FILE__"/PadToShorterLength", "[Strings][PadLeft]")
+{
+    // Setup
+    const std::string in = "hello";
+
+    // Exercise
+    const std::string out = StringTools::PadLeft(in, '0', 3);
+
+    // Verify
+    REQUIRE(out == "hello");
+    return;
+}
+
+// Tests that padding to a length equal adds no padding 
+TEST_CASE(__FILE__"/PadToEqualLength", "[Strings][PadLeft]")
+{
+  // Setup
+  const std::string in = "hello";
+
+  // Exercise
+  const std::string out = StringTools::PadLeft(in, '0', 5);
+
+  // Verify
+  REQUIRE(out == "hello");
+  return;
+}
+
+// Tests that adding padding works
+TEST_CASE(__FILE__"/Padding", "[Strings][PadLeft]")
+{
+    // Setup
+    const std::string in = "hello";
+
+    // Exercise
+    const std::string out = StringTools::PadLeft(in, '0', 7);
+
+    // Verify
+    REQUIRE(out == "00hello");
+    return;
+}