AbstractMethodUnitTest: add "tear down" method to reset static proper…

…ties

... to prevent changes to the values of these for one test, influencing another test.

This is only a stability tweak, there are no existing tests affected by this issue at this time.

tests/Core/AbstractMethodUnitTest.php

@@ -80,6 +80,25 @@ public static function initializeFile()
     }//end initializeFile()
 
 
+    /**
+     * Clean up after finished test by resetting all static properties on the class to their default values.
+     *
+     * Note: This is a PHPUnit cross-version compatible {@see \PHPUnit\Framework\TestCase::tearDownAfterClass()}
+     * method.
+     *
+     * @afterClass
+     *
+     * @return void
+     */
+    public static function reset()
+    {
+        self::$fileExtension = 'inc';
+        self::$tabWidth      = 4;
+        self::$phpcsFile     = null;
+
+    }//end reset()
+
+
     /**
      * Get the token pointer for a target token based on a specific comment found on the line before.
      *