diff --git a/iron-test-helpers.html b/iron-test-helpers.html
index 225680b..b5678b9 100644
--- a/iron-test-helpers.html
+++ b/iron-test-helpers.html
@@ -9,15 +9,3 @@
 -->
 <link rel="import" href="mock-interactions.html">
 <link rel="import" href="test-helpers.html">
-<script>
-  (function(global) {
-    'use strict';
-
-    var TestHelpers = global.TestHelpers = global.TestHelpers || {};
-
-    TestHelpers.flushAsynchronousOperations = flushAsynchronousOperations;
-    TestHelpers.forceXIfStamp = forceXIfStamp;
-    TestHelpers.fireEvent = fireEvent;
-    TestHelpers.skipUnless = skipUnless;
-  })(this);
-</script>
diff --git a/mock-interactions.js b/mock-interactions.js
index 1c880cf..60ab3f1 100644
--- a/mock-interactions.js
+++ b/mock-interactions.js
@@ -27,10 +27,10 @@
     return has;
   })();
 
-  /*
+  /**
    * Returns the (x,y) coordinates representing the middle of a node.
    *
-   * @param {HTMLElement} node An element.
+   * @param {!HTMLElement} node An element.
    */
   function middleOfNode(node) {
     var bcr = node.getBoundingClientRect();
@@ -40,10 +40,10 @@
     };
   }
 
-  /*
+  /**
    * Returns the (x,y) coordinates representing the top left corner of a node.
    *
-   * @param {HTMLElement} node An element.
+   * @param {!HTMLElement} node An element.
    */
   function topLeftOfNode(node) {
     var bcr = node.getBoundingClientRect();
@@ -58,8 +58,8 @@
    * and a target node. The Touch instances will each have a unique Touch
    * identifier.
    *
-   * @param {Array} xyList A list of (x,y) coordinate objects.
-   * @param {HTMLElement} node A target element node.
+   * @param {!Array<{ x: number, y: number }>} xyList A list of (x,y) coordinate objects.
+   * @param {!HTMLElement} node A target element node.
    */
   function makeTouches(xyList, node) {
     var id = 0;
@@ -83,11 +83,11 @@
    * @param {string} type The type of TouchEvent to generate.
    * @param {{ x: number, y: number }} xy An (x,y) coordinate for the generated
    * TouchEvent.
-   * @param {HTMLElement} node The target element node for the generated
+   * @param {!HTMLElement} node The target element node for the generated
    * TouchEvent to be dispatched on.
    */
   function makeSoloTouchEvent(type, xy, node) {
-    var xy = xy || middleOfNode(node);
+    xy = xy || middleOfNode(node);
     var touches = makeTouches([xy], node);
     var touchEventInit = {
       touches: touches,
@@ -108,13 +108,13 @@
     node.dispatchEvent(event);
   }
 
-  /*
+  /**
    * Fires a mouse event on a specific node, at a given set of coordinates.
    * This event bubbles and is cancellable.
    *
    * @param {string} type The type of mouse event (such as 'tap' or 'down').
-   * @param {Object} xy The (x,y) coordinates the mouse event should be fired from.
-   * @param {HTMLElement} node The node to fire the event on.
+   * @param {{ x: number, y: number }} xy The (x,y) coordinates the mouse event should be fired from.
+   * @param {!HTMLElement} node The node to fire the event on.
    */
   function makeMouseEvent(type, xy, node) {
     var props = {
@@ -147,14 +147,14 @@
     node.dispatchEvent(e);
   }
 
-  /*
+  /**
    * Simulates a mouse move action by firing a `move` mouse event on a
    * specific node, between a set of coordinates.
    *
-   * @param {HTMLElement} node The node to fire the event on.
+   * @param {!HTMLElement} node The node to fire the event on.
    * @param {Object} fromXY The (x,y) coordinates the dragging should start from.
    * @param {Object} toXY The (x,y) coordinates the dragging should end at.
-   * @param {?Object} steps Optional. The numbers of steps in the move motion.
+   * @param {?number} steps Optional. The numbers of steps in the move motion.
    *    If not specified, the default is 5.
    */
   function move(node, fromXY, toXY, steps) {
@@ -176,13 +176,13 @@
     }, node);
   }
 
-  /*
+  /**
    * Simulates a mouse dragging action originating in the middle of a specific node.
    *
-   * @param {HTMLElement} target The node to fire the event on.
+   * @param {!HTMLElement} target The node to fire the event on.
    * @param {?number} dx The horizontal displacement.
    * @param {?number} dy The vertical displacement
-   * @param {?Object} steps Optional. The numbers of steps in the dragging motion.
+   * @param {?number} steps Optional. The numbers of steps in the dragging motion.
    *    If not specified, the default is 5.
    */
   function track(target, dx, dy, steps) {
@@ -199,26 +199,26 @@
     up(target, xy2);
   }
 
-  /*
+  /**
    * Fires a `down` mouse event on a specific node, at a given set of coordinates.
    * This event bubbles and is cancellable. If the (x,y) coordinates are
    * not specified, the middle of the node will be used instead.
    *
-   * @param {HTMLElement} node The node to fire the event on.
-   * @param {?Object} xy Optional. The (x,y) coordinates the mouse event should be fired from.
+   * @param {!HTMLElement} node The node to fire the event on.
+   * @param {{ x: number, y: number }=} xy Optional. The (x,y) coordinates the mouse event should be fired from.
    */
   function down(node, xy) {
     xy = xy || middleOfNode(node);
     makeMouseEvent('mousedown', xy, node);
   }
 
-  /*
+  /**
    * Fires an `up` mouse event on a specific node, at a given set of coordinates.
    * This event bubbles and is cancellable. If the (x,y) coordinates are
    * not specified, the middle of the node will be used instead.
    *
-   * @param {HTMLElement} node The node to fire the event on.
-   * @param {?Object} xy Optional. The (x,y) coordinates the mouse event should be fired from.
+   * @param {!HTMLElement} node The node to fire the event on.
+   * @param {{ x: number, y: number }=} xy Optional. The (x,y) coordinates the mouse event should be fired from.
    */
   function up(node, xy) {
     xy = xy || middleOfNode(node);
@@ -227,8 +227,8 @@
 
   /**
    * Generate a click event on a given node, optionally at a given coordinate.
-   * @param {HTMLElement} node The node to fire the click event on.
-   * @param {?Object} xy Optional. The (x,y) coordinates the mouse event should
+   * @param {!HTMLElement} node The node to fire the click event on.
+   * @param {{ x: number, y: number }=} xy Optional. The (x,y) coordinates the mouse event should
    * be fired from.
    */
   function click(node, xy) {
@@ -238,8 +238,8 @@
 
   /**
    * Generate a touchstart event on a given node, optionally at a given coordinate.
-   * @param {HTMLElement} node The node to fire the click event on.
-   * @param {?Object} xy Optional. The (x,y) coordinates the touch event should
+   * @param {!HTMLElement} node The node to fire the click event on.
+   * @param {{ x: number, y: number }=} xy Optional. The (x,y) coordinates the touch event should
    * be fired from.
    */
   function touchstart(node, xy) {
@@ -250,8 +250,8 @@
 
   /**
    * Generate a touchend event on a given node, optionally at a given coordinate.
-   * @param {HTMLElement} node The node to fire the click event on.
-   * @param {?Object} xy Optional. The (x,y) coordinates the touch event should
+   * @param {!HTMLElement} node The node to fire the click event on.
+   * @param {{ x: number, y: number }=} xy Optional. The (x,y) coordinates the touch event should
    * be fired from.
    */
   function touchend(node, xy) {
@@ -259,13 +259,13 @@
     makeSoloTouchEvent('touchend', xy, node);
   }
 
-  /*
+  /**
    * Simulates a complete mouse click by firing a `down` mouse event, followed
    * by an asynchronous `up` and `tap` events on a specific node. Calls the
    *`callback` after the `tap` event is fired.
    *
-   * @param {HTMLElement} target The node to fire the event on.
-   * @param {?Object} callback Optional. The function to be called after the action ends.
+   * @param {!HTMLElement} target The node to fire the event on.
+   * @param {?Function} callback Optional. The function to be called after the action ends.
    * @param {?{
    *   emulateTouch: boolean
    * }} options Optional. Configure the emulation fidelity of the mouse events.
@@ -284,11 +284,11 @@
     });
   }
 
-  /*
+  /**
    * Fires a 'tap' mouse event on a specific node. This respects the pointer-events
    * set on the node, and will not fire on disabled nodes.
    *
-   * @param {HTMLElement} node The node to fire the event on.
+   * @param {!HTMLElement} node The node to fire the event on.
    * @param {?{
    *   emulateTouch: boolean
    * }} options Optional. Configure the emulation fidelity of the mouse event.
@@ -310,10 +310,10 @@
     click(node, xy);
   }
 
-  /*
+  /**
    * Focuses a node by firing a `focus` event. This event does not bubble.
    *
-   * @param {HTMLElement} target The node to fire the event on.
+   * @param {!HTMLElement} target The node to fire the event on.
    */
   function focus(target) {
     Polymer.Base.fire('focus', {}, {
@@ -322,10 +322,10 @@
     });
   }
 
-  /*
+  /**
    * Blurs a node by firing a `blur` event. This event does not bubble.
    *
-   * @param {HTMLElement} target The node to fire the event on.
+   * @param {!HTMLElement} target The node to fire the event on.
    */
   function blur(target) {
     Polymer.Base.fire('blur', {}, {
@@ -334,12 +334,12 @@
     });
   }
 
-  /*
+  /**
    * Returns a keyboard event. This event bubbles and is cancellable.
    *
    * @param {string} type The type of keyboard event (such as 'keyup' or 'keydown').
    * @param {number} keyCode The keyCode for the event.
-   * @param {?string|[string]} modifiers The key modifiers for the event.
+   * @param {(string|Array<string>)=} modifiers The key modifiers for the event.
    * Accepted values are shift, ctrl, alt, meta.
    */
   function keyboardEventFor(type, keyCode, modifiers) {
@@ -363,50 +363,50 @@
     return event;
   }
 
-  /*
+  /**
    * Fires a keyboard event on a specific node. This event bubbles and is cancellable.
    *
-   * @param {HTMLElement} target The node to fire the event on.
+   * @param {!HTMLElement} target The node to fire the event on.
    * @param {string} type The type of keyboard event (such as 'keyup' or 'keydown').
    * @param {number} keyCode The keyCode for the event.
-   * @param {?string|[string]} modifiers The key modifiers for the event.
+   * @param {(string|Array<string>)=} modifiers The key modifiers for the event.
    * Accepted values are shift, ctrl, alt, meta.
    */
   function keyEventOn(target, type, keyCode, modifiers) {
     target.dispatchEvent(keyboardEventFor(type, keyCode, modifiers));
   }
 
-  /*
+  /**
    * Fires a 'keydown' event on a specific node. This event bubbles and is cancellable.
    *
-   * @param {HTMLElement} target The node to fire the event on.
+   * @param {!HTMLElement} target The node to fire the event on.
    * @param {number} keyCode The keyCode for the event.
-   * @param {?string|[string]} modifiers The key modifiers for the event.
+   * @param {(string|Array<string>)=} modifiers The key modifiers for the event.
    * Accepted values are shift, ctrl, alt, meta.
    */
   function keyDownOn(target, keyCode, modifiers) {
     keyEventOn(target, 'keydown', keyCode, modifiers);
   }
 
-  /*
+  /**
    * Fires a 'keyup' event on a specific node. This event bubbles and is cancellable.
    *
-   * @param {HTMLElement} target The node to fire the event on.
+   * @param {!HTMLElement} target The node to fire the event on.
    * @param {number} keyCode The keyCode for the event.
-   * @param {?string|[string]} modifiers The key modifiers for the event.
+   * @param {(string|Array<string>)=} modifiers The key modifiers for the event.
    * Accepted values are shift, ctrl, alt, meta.
    */
   function keyUpOn(target, keyCode, modifiers) {
     keyEventOn(target, 'keyup', keyCode, modifiers);
   }
 
-  /*
+  /**
    * Simulates a complete key press by firing a `keydown` keyboard event, followed
    * by an asynchronous `keyup` event on a specific node.
    *
-   * @param {HTMLElement} target The node to fire the event on.
+   * @param {!HTMLElement} target The node to fire the event on.
    * @param {number} keyCode The keyCode for the event.
-   * @param {?string|[string]} modifiers The key modifiers for the event.
+   * @param {(string|Array<string>)=} modifiers The key modifiers for the event.
    * Accepted values are shift, ctrl, alt, meta.
    */
   function pressAndReleaseKeyOn(target, keyCode, modifiers) {
@@ -416,21 +416,21 @@
     }, 1);
   }
 
-  /*
+  /**
    * Simulates a complete 'enter' key press by firing a `keydown` keyboard event,
    * followed by an asynchronous `keyup` event on a specific node.
    *
-   * @param {HTMLElement} target The node to fire the event on.
+   * @param {!HTMLElement} target The node to fire the event on.
    */
   function pressEnter(target) {
     pressAndReleaseKeyOn(target, 13);
   }
 
-  /*
+  /**
    * Simulates a complete 'space' key press by firing a `keydown` keyboard event,
    * followed by an asynchronous `keyup` event on a specific node.
    *
-   * @param {HTMLElement} target The node to fire the event on.
+   * @param {!HTMLElement} target The node to fire the event on.
    */
   function pressSpace(target) {
     pressAndReleaseKeyOn(target, 32);
diff --git a/test-helpers.js b/test-helpers.js
index b48bbb9..7507b18 100644
--- a/test-helpers.js
+++ b/test-helpers.js
@@ -10,7 +10,8 @@
 (function(global) {
   'use strict';
 
-  /*
+
+  /**
    * Forces distribution of light children, and lifecycle callbacks on the
    * Custom Elements polyfill. Used when testing elements that rely on their
    * distributed children.
@@ -22,7 +23,7 @@
     window.CustomElements && window.CustomElements.takeRecords();
   };
 
-  /*
+  /**
    * Stamps and renders a `dom-if` template.
    *
    * @param {HTMLElement} node The node containing the template,
@@ -36,10 +37,10 @@
     global.flushAsynchronousOperations();
   };
 
-  /*
+  /**
    * Fires a custom event on a specific node. This event bubbles and is cancellable.
    *
-   * @param {String} type The type of event.
+   * @param {string} type The type of event.
    * @param {Object} props Any custom properties the event contains.
    * @param {HTMLElement} node The node to fire the event on.
    */
@@ -54,7 +55,7 @@
     node.dispatchEvent(event);
   };
 
-  /*
+  /**
    * Skips a test unless a condition is met. Sample use:
    *    function isNotIE() {
    *      return !navigator.userAgent.match(/MSIE/i);
@@ -63,7 +64,7 @@
    *      ...
    *    });
    *
-   * @param {String} condition The name of a Boolean function determining if the test should be run.
+   * @param {Function} condition The name of a Boolean function determining if the test should be run.
    * @param {Function} test The test to be run.
    */
 
@@ -86,4 +87,11 @@
       return result;
     };
   };
+
+  global.TestHelpers = {
+    flushAsynchronousOperations: global.flushAsynchronousOperations,
+    forceXIfStamp: global.forceXIfStamp,
+    fireEvent: global.fireEvent,
+    skipUnless: global.skipUnless
+  };
 })(this);