First TwoPlayerTrueSkillCalculator unit test passed

PHPSkills/Guard.php

@@ -0,0 +1,35 @@
+<?php
+namespace Moserware\Skills;
+
+/// <summary>
+/// Verifies argument contracts.
+/// </summary>
+/// <remarks>These are used until .NET 4.0 ships with Contracts. For more information,
+/// see http://www.moserware.com/2008/01/borrowing-ideas-from-3-interesting.html</remarks>
+class Guard
+{
+    public static function argumentNotNull($value, $parameterName)
+    {
+        if ($value == null)
+        {
+            throw new Exception($parameterName . " can not be null");
+        }
+    }
+
+    public static function argumentIsValidIndex($index, $count, $parameterName)
+    {
+        if (($index < 0) || ($index >= $count))
+        {
+            throw new Exception($parameterName . " is an invalid index");
+        }
+    }
+
+    public static function argumentInRangeInclusive($value, $min, $max, $parameterName)
+    {
+        if (($value < $min) || ($value > $max))
+        {
+            throw new Exception($parameterName . " is not in the valid range [" . $min . ", " . $max . "]");
+        }
+    }
+}
+?>