PP-11288-Improve Validation on Prefilled Payment Links

- Added Cypress Tests

test/cypress/integration/payment-links/amount.cy.js

@@ -47,6 +47,18 @@ describe('Amount page', () => {
       cy.get('[data-cy=error-message]').should('contain', 'Enter an amount in pounds and pence using digits and a decimal point, like 123.45 or 156.00')
     })
 
+    it('when the amount is £0.00, should display an error', () => {
+      cy.visit('/pay/a-product-id/amount')
+      cy.get('[data-cy=input]').type('0.00', { delay: 0 })
+      cy.get('[data-cy=button]').click()
+
+      cy.get('[data-cy=error-summary] a')
+        .should('contain', 'Amount must be £0.01 or more')
+        .should('have.attr', 'href', '#payment-amount')
+
+      cy.get('[data-cy=error-message]').should('contain', 'Amount must be £0.01 or more')
+    })
+
     it('when a valid amount is entered, should then go to the `confirm` page', () => {
       cy.visit('/pay/a-product-id/amount')
       cy.get('[data-cy=input]')

test/cypress/integration/payment-links/details-provided-in-query-params.cy.js

@@ -55,6 +55,29 @@ describe('Payment link visited with amount and reference provided as query param
       })
     })
   })
+
+  it('should show error page when confirmation page has a £0 amount and the "Continue to payment" button is clicked', () => {
+    cy.visit(`/redirect/${serviceNamePath}/${productNamePath}?amount=0&reference=REF123`)
+    cy.get('h1').should('have.text', productName)
+
+    cy.get('[data-cy=button]').click()
+
+    cy.location().should((location) => {
+      expect(location.pathname).to.eq(`/pay/${productExternalId}/confirm`)
+    })
+
+    cy.get('.govuk-summary-list__row').eq(1).within(() => {
+      cy.get('dt').should('contain', 'Total to pay')
+      cy.get('dd').eq(0).should('contain', '£0')
+      // should have no change link
+      cy.get('dd').eq(1).should('not.exist')
+    })
+
+    cy.get('[data-cy=continue-to-payment-button]').click()
+    cy.get('h1').should('have.text', 'An error occurred:')
+    cy.get('[data-cy=error-message]').should('have.text', 'There is a problem with the link you have been sent to use to pay. ' +
+      'The payment amount cannot be £0.00. Contact the service you’re trying to make a payment to.')
+  })
 })
 
 describe('Payment link visited with invalid amount in query params', () => {
@@ -91,4 +114,4 @@ describe('Payment link visited with invalid reference in query params', () => {
     cy.get('h1').should('have.text', 'An error occurred:')
     cy.get('[data-cy=error-message]').should('have.text', 'Please contact the service you are trying to make a payment to.')
   })
-})
+})