Add coverage testing using undercover.el

Cask

@@ -17,4 +17,5 @@
              :git "https://github.com/DarwinAwardWinner/emacs-buttercup.git"
              :branch "expect-closures"
              :files ("*.el"
-                     ("bin" "bin/*"))))
+                     ("bin" "bin/*")))
+ (depends-on "undercover"))

tests/test-ido-completing-read+.el

@@ -1,5 +1,9 @@
 ;;; -*- lexical-binding: t -*-
 
+(require 'undercover)
+(undercover "*.el"
+            (:exclude "test-*.el"))
+
 (require 'ido)
 (require 'flx-ido)
 (require 'ido-completing-read+)