Change service billing details

View page that lets you change service billing details and
update details on form submission.

tests/app/main/views/test_service_settings.py

@@ -5300,3 +5300,54 @@ def test_service_settings_links_to_edit_service_billing_details_page_for_platfor
     ))
     page = BeautifulSoup(response.data.decode('utf-8'), 'html.parser')
     assert len(page.find_all('a', attrs={'href': '/services/{}/edit-billing-details'.format(SERVICE_ONE_ID)})) == 1
+
+
+def test_view_edit_service_billing_details(
+        platform_admin_client,
+        service_one,
+
+):
+    response = platform_admin_client.get(url_for('main.edit_service_billing_details', service_id=SERVICE_ONE_ID))
+    page = BeautifulSoup(response.data.decode('utf-8'), 'html.parser')
+    assert page.select_one('h1').text == "Change service billing details"
+    labels = page.find_all('label', class_="form-label")
+    labels_list = [
+        'Billing contact email address', 'Billing contact name', 'Billing reference', 'Purchase order number'
+    ]
+    for label in labels:
+        assert label.text.strip() in labels_list
+    textbox_names = page.find_all('input', class_='govuk-input govuk-!-width-two-thirds')
+    names_list = ['billing_contact_email_address', 'billing_contact_name', 'billing_reference', 'purchase_order_number']
+
+    for name in textbox_names:
+        assert name.attrs["name"] in names_list
+
+
+def test_update_service_billing_details(
+        platform_admin_client,
+        service_one,
+        mock_update_service
+):
+    response = platform_admin_client.post(
+        url_for(
+            'main.edit_service_billing_details',
+            service_id=SERVICE_ONE_ID,
+        ),
+        data={
+            'billing_contact_email_address': 'accounts@fluff.gov.uk',
+            'billing_contact_name': 'Flannellette von Fluff',
+            'billing_reference': '',
+            'purchase_order_number': 'PO1234'
+        }
+    )
+    assert response.status_code == 302
+    settings_url = url_for(
+        'main.service_settings', service_id=SERVICE_ONE_ID, _external=True)
+    assert response.location == settings_url
+    mock_update_service.assert_called_with(
+        SERVICE_ONE_ID,
+        billing_contact_email_address='accounts@fluff.gov.uk',
+        billing_contact_name='Flannellette von Fluff',
+        billing_reference='',
+        purchase_order_number='PO1234'
+    )