When banning a user, a reason can be provided. The user will see this reason when trying to log in. Also log bans and unbans in the staff action logs.

spec/services/staff_action_logger_spec.rb

@@ -115,4 +115,39 @@ describe StaffActionLogger do
       json['header'].should == site_customization.header
     end
   end
+
+  describe "log_user_ban" do
+    let(:user) { Fabricate(:user) }
+
+    it "raises an error when arguments are missing" do
+      expect { logger.log_user_ban(nil, nil) }.to raise_error(Discourse::InvalidParameters)
+      expect { logger.log_user_ban(nil, "He was bad.") }.to raise_error(Discourse::InvalidParameters)
+    end
+
+    it "reason arg is optional" do
+      expect { logger.log_user_ban(user, nil) }.to_not raise_error
+    end
+
+    it "creates a new UserHistory record" do
+      reason = "He was a big meanie."
+      log_record = logger.log_user_ban(user, reason)
+      log_record.should be_valid
+      log_record.details.should == reason
+      log_record.target_user.should == user
+    end
+  end
+
+  describe "log_user_unban" do
+    let(:user) { Fabricate(:user, banned_at: 1.day.ago, banned_till: 7.days.from_now) }
+
+    it "raises an error when argument is missing" do
+      expect { logger.log_user_unban(nil) }.to raise_error(Discourse::InvalidParameters)
+    end
+
+    it "creates a new UserHistory record" do
+      log_record = logger.log_user_unban(user)
+      log_record.should be_valid
+      log_record.target_user.should == user
+    end
+  end
 end