Show count of other users signing in with an IP

Helps to identify possible misusers.

app/models/user/sign_in.rb

@@ -32,6 +32,10 @@ def self.retention_days
     AlaveteliConfiguration.user_sign_in_activity_retention_days
   end
 
+  def other_users
+    self.class.where(ip: ip).where.not(user_id: user_id)
+  end
+
   private
 
   def create?

app/views/admin/users/_sign_in_table.html.erb

@@ -10,6 +10,10 @@
       </td>
 
       <td><%= admin_date(sign_in.created_at, ago_only: true) %></td>
+
+      <td>
+        <strong><%= sign_in.other_users.size %></strong> others using this IP
+      </td>
     </tr>
   <% end %>
 </table>

spec/models/user/sign_in_spec.rb

@@ -83,6 +83,29 @@
     end
   end
 
+  describe '#other_users' do
+    subject { sign_in.other_users }
+
+    before do
+      allow(AlaveteliConfiguration).
+        to receive(:user_sign_in_activity_retention_days).and_return(1)
+    end
+
+    let(:sign_in_1) { FactoryBot.create(:user_sign_in, ip: '1.1.1.1') }
+    let(:sign_in_2) { FactoryBot.create(:user_sign_in, ip: '1.1.1.1') }
+    let(:sign_in_3) { FactoryBot.create(:user_sign_in, ip: '2.2.2.2') }
+
+    context 'when there are other users using the same IP' do
+      let(:sign_in) { sign_in_1 }
+      it { is_expected.to match_array([sign_in_2]) }
+    end
+
+    context 'when there are no other users using the same IP' do
+      let(:sign_in) { sign_in_3 }
+      it { is_expected.to be_empty }
+    end
+  end
+
   describe '#save' do
     subject { sign_in.save }