Handle delivery error in CBV Flow Invitations Controller

When there is a delivery error, let's catch it and give the user a
better error message.

In order to test this in development, you'll need to set
`config.action_mailer.raise_delivery_errors` to true. (It's true by
default in production.)

Finishes FFS-839.

app/app/controllers/cbv_flow_invitations_controller.rb

@@ -6,10 +6,19 @@ def new
   end
 
   def create
-    CbvInvitationService.new.invite(
-      cbv_flow_invitation_params[:email_address],
-      cbv_flow_invitation_params[:case_number]
-    )
+    begin
+      CbvInvitationService.new.invite(
+        cbv_flow_invitation_params[:email_address],
+        cbv_flow_invitation_params[:case_number]
+      )
+    rescue => ex
+      flash[:alert] = t(".invite_failed",
+                        email_address: cbv_flow_invitation_params[:email_address],
+                        error_message: ex.message
+                       )
+      Rails.logger.error("Error sending CBV invitation: #{ex.class} - #{ex.message}")
+      return redirect_to new_cbv_flow_invitation_path(secret: params[:secret])
+    end
 
     flash[:notice] = t(".invite_success", email_address: cbv_flow_invitation_params[:email_address])
     redirect_to root_url

app/config/locales/en.yml

@@ -8,6 +8,7 @@ en:
       thank_you: Thank you!
   cbv_flow_invitations:
     create:
+      invite_failed: 'Error sending invitation to %{email_address}: %{error_message}.'
       invite_success: Successfully delivered invitation to %{email_address}.
     incorrect_invite_secret: Unable to send invitation due to missing invitation secret parameter.
     new:

app/spec/controllers/cbv_flow_invitations_controller_spec.rb

@@ -71,6 +71,32 @@
 
         expect(response).to redirect_to(root_url)
       end
+
+      context "when the CbvInvitationService has an error" do
+        let(:broken_params) do
+          valid_params.tap do |params|
+            params[:cbv_flow_invitation][:email_address] = "bad-email@"
+          end
+        end
+
+        before do
+          allow_any_instance_of(CbvInvitationService)
+            .to receive(:invite)
+            .with("bad-email@", "ABC1234")
+            .and_raise(StandardError.new("Some random error, like a bad email address or something."))
+        end
+
+        it "redirects back to the invitation form with the error" do
+          expect_any_instance_of(CbvInvitationService)
+            .to receive(:invite)
+            .with("bad-email@", "ABC1234")
+
+          post :create, params: broken_params
+
+          expect(response).to redirect_to(new_cbv_flow_invitation_path(secret: broken_params[:secret]))
+          expect(controller.flash.alert).to include("Some random error")
+        end
+      end
     end
   end
 end