Tried mocking proc_open function for coverage

Signed-off-by: Tom Van Herreweghe <tom@king-foo.be>

Author: Tom Van Herreweghe

tests/PHPExif/Adapter/ExiftoolProcOpenTest.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace PHPExif\Tests\Adapter {
+
+    function proc_open()
+    {
+        return false;
+    }
+
+    include __DIR__ . '/../../../lib/PHPExif/Adapter/Exiftool.php';
+
+    /**
+     * @covers \PHPExif\Adapter\Exiftool::<!public>
+     */
+    class ExiftoolProcOpenTest extends \PHPUnit_Framework_TestCase
+    {
+        /**
+         * @var \PHPExif\Adapter\Exiftool
+         */
+        protected $adapter;
+
+        public function setUp()
+        {
+            $this->adapter = new \PHPExif\Adapter\Exiftool();
+        }
+        /**
+         * @group exiftool
+         * @covers \PHPExif\Adapter\Exiftool::getCliOutput
+         */
+        public function testGetCliOutput()
+        {
+            $reflMethod = new \ReflectionMethod('\PHPExif\Adapter\Exiftool', 'getCliOutput');
+            $reflMethod->setAccessible(true);
+
+            $result = $reflMethod->invoke(
+                $this->adapter,
+                sprintf(
+                    '%1$s',
+                    'pwd'
+                )
+            );
+
+            $this->assertInternalType('string', $result);
+        }
+    }
+}