added new test and fixed test

Author: KevinGrajeda

src/math/trigonometry.js

@@ -284,7 +284,6 @@ p5.prototype.radians = angle => angle * constants.DEG_TO_RAD;
  * Calling <a href="#/p5/angleMode">angleMode()</a> with no arguments returns current anglemode.
  * @method angleMode
  * @param {Constant} mode either RADIANS or DEGREES
- * @chainable
  * @example
  * <div>
  * <code>
@@ -318,7 +317,6 @@ p5.prototype.angleMode = function(mode) {
   } else if (mode === constants.DEGREES || mode === constants.RADIANS) {
     this._angleMode = mode;
   }
-  return this;
 };
 
 /**