Service name uniqueness handled in all cases and tests passing.

app/main/forms.py

@@ -205,7 +205,24 @@ class AddServiceForm(Form):
 
 
 class ServiceNameForm(Form):
-    name = StringField(u'New name')
+    def __init__(self, names_func, *args, **kwargs):
+        """
+        Keyword arguments:
+        names_func -- Returns a list of unique service_names already registered
+        on the system.
+        """
+        self._names_func = names_func
+        super(ServiceNameForm, self).__init__(*args, **kwargs)
+
+    name = StringField(
+        u'New name',
+        validators=[
+            DataRequired(message='Service name can’t be empty')
+        ])
+
+    def validate_name(self, a):
+        if a.data in self._names_func():
+            raise ValidationError('This service name is already in use')
 
 
 class ConfirmPasswordForm(Form):

app/main/views/service_settings.py

@@ -18,7 +18,8 @@ from notifications_python_client.errors import HTTPError
 from app.main.dao.services_dao import (
     get_service_by_id,
     delete_service,
-    update_service
+    update_service,
+    find_all_service_names
 )
 
 from app.main import main
@@ -57,7 +58,7 @@ def service_name_change(service_id):
         else:
             raise e
 
-    form = ServiceNameForm()
+    form = ServiceNameForm(find_all_service_names)
 
     if form.validate_on_submit():
         session['service_name_change'] = form.name.data
@@ -89,10 +90,20 @@ def service_name_change_confirm(service_id):
 
     if form.validate_on_submit():
         service['name'] = session['service_name_change']
-        update_service(service)
-        session['service_name'] = service['name']
-        session.pop('service_name_change')
-        return redirect(url_for('.service_settings', service_id=service_id))
+        try:
+            update_service(service)
+        except HTTPError as e:
+            error_msg = "Duplicate service name '{}'".format(session['service_name_change'])
+            if e.status_code == 400 and error_msg in e.message['name']:
+                # Redirect the user back to the change service name screen
+                flash('This service name is already in use', 'error')
+                return redirect(url_for('main.service_name_change', service_id=service_id))
+            else:
+                raise e
+        else:
+            session['service_name'] = service['name']
+            session.pop('service_name_change')
+            return redirect(url_for('.service_settings', service_id=service_id))
     return render_template(
         'views/service-settings/confirm.html',
         heading='Change your service name',