Added spec

spec/models/tag_spec.rb

@@ -1,5 +1,14 @@
 require 'rails_helper'
 
 RSpec.describe Tag, type: :model do
-  pending "add some examples to (or delete) #{__FILE__}"
+  it 'sets lowercase_name on save' do
+    t = Tag.new(name: 'Tag')
+    expect(t.name).to eq 'Tag'
+    expect(t.lowercase_name).to be_nil
+
+    t.save
+
+    expect(t.name).to eq 'Tag'
+    expect(t.lowercase_name).to eq 'tag'
+  end
 end