DEV: Add simplecov as test dependency (#7271)

Gemfile

@@ -121,6 +121,7 @@ group :test do
   gem 'fakeweb', '~> 1.3.0', require: false
   gem 'minitest', require: false
   gem 'danger'
+  gem 'simplecov', require: false
 end
 
 group :test, :development do

Gemfile.lock

@@ -115,6 +115,7 @@ GEM
       image_size (~> 1.5)
       in_threads (~> 1.3)
       progress (~> 3.0, >= 3.0.1)
+    docile (1.3.1)
     email_reply_trimmer (0.1.12)
     ember-data-source (3.0.2)
       ember-source (>= 2, < 3.0)
@@ -170,6 +171,7 @@ GEM
       rails-dom-testing (>= 1, < 3)
       railties (>= 4.2.0)
       thor (>= 0.14, < 2.0)
+    json (2.2.0)
     jwt (2.1.0)
     kgio (2.11.2)
     kramdown (1.17.0)
@@ -407,6 +409,11 @@ GEM
       rack (>= 1.5.0)
       rack-protection (>= 1.5.0)
       redis (>= 3.3.5, < 5)
+    simplecov (0.16.1)
+      docile (~> 1.1)
+      json (>= 1.8, < 3)
+      simplecov-html (~> 0.10.0)
+    simplecov-html (0.10.2)
     slop (3.6.0)
     sprockets (3.7.2)
       concurrent-ruby (~> 1.0)
@@ -549,6 +556,7 @@ DEPENDENCIES
   seed-fu
   shoulda
   sidekiq
+  simplecov
   sprockets-rails
   sshkey
   stackprof