Add an isDate test for Invalid Date

Author: leshakoss

src/isDate/index.js

@@ -17,12 +17,17 @@
  * //=> true
  *
  * @example
- * // For a value
+ * // For an invalid date:
+ * var result = isDate(new Date(NaN))
+ * //=> true
+ *
+ * @example
+ * // For some value:
  * var result = isDate('2014-02-31')
  * //=> false
  *
  * @example
- * // For a object
+ * // For an object:
  * var result = isDate({})
  * //=> false
  */

src/isDate/test.js

@@ -10,6 +10,10 @@ describe('isDate', function () {
     assert(isDate(new Date()))
   })
 
+  it('returns true if the given value is an Invalid Date', function () {
+    assert(isDate(new Date(NaN)))
+  })
+
   context('with date passed from another iframe', function () {
     afterEach(function () {
       const iframe = document.getElementById('iframe')