[TECH] Add the infite decimal method and tests

Author: codisart

src/InfiniteDecimal.php

@@ -311,6 +311,20 @@ public function sin($scale = null)
         );
     }
 
+    /**
+     * Throws exception because cosecant is undefined in the infinite.
+     *
+     * @param integer $scale
+     * @return null
+     */
+    public function cosec($scale = null)
+    {
+        throw new \DomainException(($this === self::$pInf) ?
+            "Cosecant function hasn't limit in the positive infinite." :
+            "Cosecant function hasn't limit in the negative infinite."
+        );
+    }
+
     /**
      * Throws exception because cosine is undefined in the infinite.
      *

tests/InfiniteDecimal/InfiniteDecimalCosecTest.php

@@ -0,0 +1,27 @@
+<?php
+
+use Litipk\BigNumbers\InfiniteDecimal as InfiniteDecimal;
+
+/**
+ * @group cos
+ */
+class InfiniteDecimalCosecTest extends PHPUnit_Framework_TestCase
+{
+    /**
+     * @expectedException \DomainException
+     * @expectedExceptionMessage Cosecant function hasn't limit in the positive infinite.
+     */
+    public function testFinitePositiveInfiniteCosec()
+    {
+        InfiniteDecimal::getPositiveInfinite()->cosec();
+    }
+
+    /**
+     * @expectedException \DomainException
+     * @expectedExceptionMessage Cosecant function hasn't limit in the negative infinite.
+     */
+    public function testFiniteNegativeInfiniteCosec()
+    {
+        InfiniteDecimal::getNegativeInfinite()->cosec();
+    }
+}