Fix for duplicate email registration that meant flash error not being

displayed.

The error message does not specify the error is a duplicate email
address so as not to reveal which emails are current user accounts.

tests/app/main/views/test_register.py

@@ -1,4 +1,5 @@
 from flask import url_for
+from bs4 import BeautifulSoup
 
 
 def test_render_register_returns_template_with_form(app_):
@@ -106,3 +107,24 @@ def test_should_return_400_if_password_is_blacklisted(app_,
 
     response.status_code == 200
     assert 'That password is blacklisted, too common' in response.get_data(as_text=True)
+
+
+def test_register_with_existing_email_returns_error(app_,
+                                                    api_user_active,
+                                                    mock_get_user_by_email):
+    user_data = {
+        'name': 'Already Hasaccount',
+        'email_address': api_user_active.email_address,
+        'mobile_number': '+4407700900460',
+        'password': 'validPassword!'
+    }
+
+    with app_.test_request_context():
+        response = app_.test_client().post(url_for('main.register'),
+                                           data=user_data)
+        assert response.status_code == 200
+        page = BeautifulSoup(response.data.decode('utf-8'), 'html.parser')
+        element = page.find('h1')
+        assert element.text == 'Create an account'
+        flash_banner = page.find('div', class_='banner-dangerous').string.strip()
+        assert flash_banner == 'There was an error registering your account'