Address checkout spec race conditions

We want to avoid clicking the same 'Save and Continue' button three
times in a row, so we've added assertions that make sure we have
navigated to the next page before trying to click it again.

Co-authored-by: Jared Norman <jared@super.gd>

Author: senemsoy

spec/features/checkout_spec.rb

@@ -63,7 +63,12 @@
       fill_addresses_fields_with(address)
       click_button 'Save and Continue'
 
+      expect(page).to have_content 'UPS Ground'
+
       click_button 'Save and Continue'
+
+      expect(page).to have_content(/Payment Information/i)
+
       click_button 'Save and Continue'
       click_button 'Place Order'
 
@@ -89,7 +94,12 @@
       fill_addresses_fields_with(address)
       click_button 'Save and Continue'
 
+      expect(page).to have_content 'UPS Ground'
+
       click_button 'Save and Continue'
+
+      expect(page).to have_content(/Payment Information/i)
+
       click_button 'Save and Continue'
       click_button 'Place Order'
 
@@ -145,9 +155,15 @@
       expect(page).to have_text 'You have signed up successfully.'
 
       fill_addresses_fields_with(address)
+
       click_button 'Save and Continue'
 
+      expect(page).to have_content 'UPS Ground'
+
       click_button 'Save and Continue'
+
+      expect(page).to have_content(/Payment Information/i)
+
       click_button 'Save and Continue'
       click_button 'Place Order'