add more tests to models

spec/models/mention_spec.rb

@@ -1,5 +1,22 @@
 require 'rails_helper'
 
 RSpec.describe Mention, type: :model do
+  describe 'validations' do
+    it 'has a valid fabricator' do
+      mention = Fabricate.build(:mention)
+      expect(mention).to be_valid
+    end
 
+    it 'is invalid without an account' do
+      mention = Fabricate.build(:mention, account: nil)
+      mention.valid?
+      expect(mention).to model_have_error_on_field(:account)
+    end
+
+    it 'is invalid without a status' do
+      mention = Fabricate.build(:mention, status: nil)
+      mention.valid?
+      expect(mention).to model_have_error_on_field(:status)
+    end
+  end
 end