Add error handler for duplicate domain

app/email_branding/rest.py

@@ -1,4 +1,5 @@
-from flask import Blueprint, jsonify, request
+from flask import Blueprint, current_app, jsonify, request
+from sqlalchemy.exc import IntegrityError
 
 from app.dao.email_branding_dao import (
     dao_create_email_branding,
@@ -18,6 +19,22 @@ email_branding_blueprint = Blueprint('email_branding', __name__)
 register_errors(email_branding_blueprint)
 
 
+@email_branding_blueprint.errorhandler(IntegrityError)
+def handle_integrity_error(exc):
+    """
+    Handle integrity errors caused by the unique constraint on domain
+    """
+    if 'domain' in str(exc):
+        return jsonify(
+            result='error',
+            message={'name': ["Duplicate domain '{}'".format(
+                exc.params.get('domain')
+            )]}
+        ), 400
+    current_app.logger.exception(exc)
+    return jsonify(result='error', message="Internal server error"), 500
+
+
 @email_branding_blueprint.route('', methods=['GET'])
 def get_email_branding_options():
     email_branding_options = [o.serialize() for o in dao_get_email_branding_options()]

tests/app/email_branding/test_rest.py

@@ -257,3 +257,30 @@ def test_update_email_branding_reject_invalid_brand_type(admin_request, notify_d
     )
 
     assert response['errors'][0]['message'] == 'brand_type NOT A TYPE is not one of [org, both, org_banner]'
+
+
+def test_400_for_duplicate_domain(admin_request, notify_db_session):
+    branding_1 = create_email_branding()
+    branding_2 = create_email_branding()
+    admin_request.post(
+        'email_branding.update_email_branding',
+        _data={'domain': 'example.com'},
+        email_branding_id=branding_1.id,
+    )
+
+    response = admin_request.post(
+        'email_branding.update_email_branding',
+        _data={'domain': 'example.com'},
+        email_branding_id=branding_2.id,
+        _expected_status=400,
+    )
+    assert response['result'] == 'error'
+    assert response['message']['name'] == ["Duplicate domain 'example.com'"]
+
+    response = admin_request.post(
+        'email_branding.create_email_branding',
+        _data={'domain': 'example.com'},
+        _expected_status=400,
+    )
+    assert response['result'] == 'error'
+    assert response['message']['name'] == ["Duplicate domain 'example.com'"]