Show validation error if user email already exists instead of crashing

app/controllers/users_controller.rb

@@ -27,16 +27,21 @@ class UsersController < ApplicationController
   def create
     @resource = User.new
     if user_params["email"].empty?
-      @resource.errors.add :email, "Enter an email address"
+      @resource.errors.add :email, I18n.t("validations.email.blank")
     elsif !email_valid?(user_params["email"])
-      @resource.errors.add :email, "Enter an email address in the correct format, like name@example.com"
+      @resource.errors.add :email, I18n.t("validations.email.invalid")
     end
     if @resource.errors.present?
       render :new, status: :unprocessable_entity
     else
-      @user = User.create!(user_params.merge(org_params).merge(password_params))
+      user = User.create(user_params.merge(org_params).merge(password_params))
-      @user.send_reset_password_instructions
+      if user.persisted?
-      redirect_to users_organisation_path(current_user.organisation)
+        user.send_reset_password_instructions
+        redirect_to users_organisation_path(current_user.organisation)
+      else
+        @resource.errors.add :email, I18n.t("validations.email.taken")
+        render :new, status: :unprocessable_entity
+      end
     end
   end
 

config/locales/en.yml

@@ -43,6 +43,10 @@ en:
       invalid_date: "Please enter a valid date"
       outside_collection_window: "Date must be within the current collection windows"
     postcode: "Enter a postcode in the correct format, for example AA1 1AA"
+    email:
+      taken: "Email already exists"
+      invalid: "Enter an email address in the correct format, like name@example.com"
+      blank: "Enter an email address"
 
     property:
       mrcdate:

spec/requests/users_controller_spec.rb

@@ -254,6 +254,44 @@ RSpec.describe UsersController, type: :request do
     end
   end
 
+  describe "#create" do
+    let(:params) do
+      {
+        "user": {
+          name: "new user",
+          email: "new_user@example.com",
+          role: "data_coordinator",
+        },
+      }
+    end
+    let(:request) { post "/users/", headers: headers, params: params }
+
+    before do
+      sign_in user
+    end
+
+    it "invites a new user" do
+      expect { request }.to change(User, :count).by(1)
+    end
+
+    it "redirects back to organisation users page" do
+      request
+      expect(response).to redirect_to("/organisations/#{user.organisation.id}/users")
+    end
+
+    context "when the email is already taken" do
+      before do
+        FactoryBot.create(:user, email: "new_user@example.com")
+      end
+
+      it "shows an error" do
+        request
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(page).to have_content(I18n.t("validations.email.taken"))
+      end
+    end
+  end
+
   describe "title link" do
     before do
       sign_in user