diff --git a/wagtail/contrib/postgres_search/tests/test_backend.py b/wagtail/contrib/postgres_search/tests/test_backend.py
index 96ceea996..50447365a 100644
--- a/wagtail/contrib/postgres_search/tests/test_backend.py
+++ b/wagtail/contrib/postgres_search/tests/test_backend.py
@@ -1,11 +1,11 @@
 from django.test import TestCase
 
-from wagtail.search.tests.test_backends import QueryAPITestMixin, BackendTests
+from wagtail.search.tests.test_backends import BackendTests
 
 from ..utils import BOOSTS_WEIGHTS, WEIGHTS_VALUES, determine_boosts_weights, get_weight
 
 
-class TestPostgresSearchBackend(QueryAPITestMixin, BackendTests, TestCase):
+class TestPostgresSearchBackend(BackendTests, TestCase):
     backend_path = 'wagtail.contrib.postgres_search.backend'
 
     def test_weights(self):
diff --git a/wagtail/search/tests/elasticsearch_common_tests.py b/wagtail/search/tests/elasticsearch_common_tests.py
index ef24f28f1..0262fece4 100644
--- a/wagtail/search/tests/elasticsearch_common_tests.py
+++ b/wagtail/search/tests/elasticsearch_common_tests.py
@@ -5,10 +5,10 @@ from django.core import management
 
 from wagtail.tests.search import models
 from wagtail.search.query import MATCH_ALL
-from wagtail.search.tests.test_backends import BackendTests, QueryAPITestMixin
+from wagtail.search.tests.test_backends import BackendTests
 
 
-class ElasticsearchCommonSearchBackendTests(QueryAPITestMixin, BackendTests):
+class ElasticsearchCommonSearchBackendTests(BackendTests):
     def test_search_with_spaces_only(self):
         # Search for some space characters and hope it doesn't crash
         results = self.backend.search("   ", models.Book)
diff --git a/wagtail/search/tests/test_backends.py b/wagtail/search/tests/test_backends.py
index 0baba13fd..92530ecc2 100644
--- a/wagtail/search/tests/test_backends.py
+++ b/wagtail/search/tests/test_backends.py
@@ -431,8 +431,6 @@ class BackendTests(WagtailTestUtils):
             "The Fellowship of the Ring"  # If this item doesn't appear, "Foundation" is still in the index
         ])
 
-
-class QueryAPITestMixin:
     #
     # Basic query classes
     #
diff --git a/wagtail/search/tests/test_db_backend.py b/wagtail/search/tests/test_db_backend.py
index 9f47912f6..fba3332d7 100644
--- a/wagtail/search/tests/test_db_backend.py
+++ b/wagtail/search/tests/test_db_backend.py
@@ -2,10 +2,10 @@ import unittest
 
 from django.test import TestCase
 
-from .test_backends import BackendTests, QueryAPITestMixin
+from .test_backends import BackendTests
 
 
-class TestDBBackend(QueryAPITestMixin, BackendTests, TestCase):
+class TestDBBackend(BackendTests, TestCase):
     backend_path = 'wagtail.search.backends.db'
 
     # Doesn't support ranking