fix tags exclude filter behaviour (#1246)

* fix tags exclude filter behaviour

taiga/base/filters.py

@@ -515,8 +515,13 @@ class TagsFilter(FilterBackend):
     def _prepare_filter_query(self, query):
         return Q(tags__contains=query)
 
-    def _prepare_exclude_query(self, query):
-        return ~Q(tags__contains=query)
+    def _prepare_exclude_query(self, tags):
+        queries = [Q(tags__contains=[tag]) for tag in tags]
+        query = queries.pop()
+        for item in queries:
+            query |= item
+
+        return ~Q(query)
 
     def filter_queryset(self, request, queryset, view):
         operations = {

tests/integration/test_issues.py

@@ -476,6 +476,18 @@ def test_api_filters(client, filter_name, collection, expected, exclude_expected
     assert len(response.data) == exclude_expected
 
 
+def test_mulitple_exclude_filter_tags(client):
+    data = create_filter_issues_context()
+    project = data["project"]
+    client.login(data["users"][0])
+    tags = data["tags"]
+
+    url = "{}?project={}&exclude_tags={},{}".format(reverse('issues-list'), project.id, tags[1], tags[2])
+    response = client.get(url)
+    assert response.status_code == 200
+    assert len(response.data) == 4
+
+
 def test_api_filters_data(client):
     data = create_filter_issues_context()
     project = data["project"]