Link to ‘who it’s for’ when error creating account

If someone enters an email address from a domain we don’t recognise we
direct them straight to our support channel. This is causing increased
contact from suppliers and members of the public.

Now that we have a page which explains who can use Notify, let’s direct
people there first. Then if they really do need to contact support
(because we don’t recognise their organisation) then they can do so from
that page.

tests/app/main/test_validators.py

@@ -36,7 +36,7 @@ def test_valid_email_not_in_valid_domains(
 ):
     form = RegisterUserForm(email_address="test@test.com", mobile_number='441231231231')
     assert not form.validate()
-    assert "Enter a government email address" in form.errors['email_address'][0]
+    assert "Enter a public sector email address" in form.errors['email_address'][0]
 
 
 def test_valid_email_in_valid_domains(

tests/app/main/views/test_manage_users.py

@@ -1192,7 +1192,7 @@ def test_edit_user_email_cannot_change_a_gov_email_address_to_a_non_gov_email_ad
         },
         _expected_status=200,
     )
-    assert 'Enter a government email address.' in page.find('span', class_='error-message').text
+    assert 'Enter a public sector email address' in page.select_one('.error-message').text
     with client_request.session_transaction() as session:
         assert 'team_member_email_change-'.format(active_user_with_permissions['id']) not in session
 

tests/app/main/views/test_register.py

@@ -7,6 +7,7 @@ from flask import session, url_for
 from flask_login import current_user
 
 from app.models.user import InvitedUser
+from tests.conftest import normalize_spaces
 
 
 def test_render_register_returns_template_with_form(client):
@@ -97,20 +98,27 @@ def test_process_register_returns_200_when_mobile_number_is_invalid(
 
 
 def test_should_return_200_when_email_is_not_gov_uk(
-    client,
-    mock_send_verify_code,
-    mock_get_user_by_email,
+    client_request,
     mock_get_organisations,
-    mock_login,
 ):
-    response = client.post(url_for('main.register'),
-                           data={'name': 'Bad Mobile',
-                                 'email_address': 'bad_mobile@example.not.right',
-                                 'mobile_number': '+44123412345',
-                                 'password': 'validPassword!'})
+    client_request.logout()
+    page = client_request.post(
+        'main.register',
+        _data={
+            'name': 'Firstname Lastname',
+            'email_address': 'bad_mobile@example.not.right',
+            'mobile_number': '07900900123',
+            'password': 'validPassword!'
+        },
+        _expected_status=200,
+    )
 
-    assert response.status_code == 200
-    assert 'Enter a government email address' in response.get_data(as_text=True)
+    assert normalize_spaces(page.select_one('.error-message').text) == (
+        'Enter a public sector email address or find out who can use Notify'
+    )
+    assert page.select_one('.error-message a')['href'] == url_for(
+        'main.who_its_for'
+    )
 
 
 @pytest.mark.parametrize('email_address', (