diff --git a/wagtail/admin/tests/pages/test_move_page.py b/wagtail/admin/tests/pages/test_move_page.py
index e2781ab56c..9d56fd081f 100644
--- a/wagtail/admin/tests/pages/test_move_page.py
+++ b/wagtail/admin/tests/pages/test_move_page.py
@@ -73,7 +73,7 @@ class TestPageMove(TestCase, WagtailTestUtils):
         # to verify that a user without bulk delete permission is able to move a page with a child page
 
         self.client.logout()
-        user = get_user_model().objects.get(username='siteeditor')
+        user = get_user_model().objects.get(email='siteeditor@example.com')
         self.login(user)
 
         # ensure the bulk_delete is not applicable to this user
diff --git a/wagtail/admin/tests/pages/test_revisions.py b/wagtail/admin/tests/pages/test_revisions.py
index 4470a75d35..a6a1cdb2d5 100644
--- a/wagtail/admin/tests/pages/test_revisions.py
+++ b/wagtail/admin/tests/pages/test_revisions.py
@@ -107,7 +107,7 @@ class TestRevisions(TestCase, WagtailTestUtils):
         editors_group = Group.objects.get(name='Site-wide editors')
         editors_group.page_permissions.update(page_id=st_patricks.id)
 
-        editor = get_user_model().objects.get(username='siteeditor')
+        editor = get_user_model().objects.get(email='siteeditor@example.com')
 
         self.login(editor)
         response = self.request_preview_revision()
diff --git a/wagtail/admin/tests/pages/test_view_draft.py b/wagtail/admin/tests/pages/test_view_draft.py
index 9d5f5b453b..98fb2aced5 100644
--- a/wagtail/admin/tests/pages/test_view_draft.py
+++ b/wagtail/admin/tests/pages/test_view_draft.py
@@ -67,7 +67,7 @@ class TestDraftAccess(TestCase, WagtailTestUtils):
     def test_draft_access_authorized(self):
         """Test that user with edit permission can view draft."""
         # give user the permission to edit page
-        user = get_user_model().objects.get(username='bob')
+        user = get_user_model().objects.get(email='bob@example.com')
         user.groups.add(Group.objects.get(name='Moderators'))
         user.save()
 
diff --git a/wagtail/admin/tests/test_account_management.py b/wagtail/admin/tests/test_account_management.py
index b84f6cd192..0d95eb7926 100644
--- a/wagtail/admin/tests/test_account_management.py
+++ b/wagtail/admin/tests/test_account_management.py
@@ -611,7 +611,7 @@ class TestAccountManagementForNonModerator(TestCase, WagtailTestUtils):
         self.submitter = self.create_user('submitter', 'submitter@example.com', 'password')
         self.submitter.groups.add(Group.objects.get(name='Editors'))
 
-        self.login(username=self.submitter.username, password='password')
+        self.login(username='submitter', password='password')
 
     def test_notification_preferences_form_is_reduced_for_non_moderators(self):
         """
@@ -640,7 +640,7 @@ class TestAccountManagementForAdminOnlyUser(TestCase, WagtailTestUtils):
         )
         self.admin_only_user.groups.add(admin_only_group)
 
-        self.login(username=self.admin_only_user.username, password='password')
+        self.login(username='admin_only_user', password='password')
 
     def test_notification_preferences_view_redirects_for_admin_only_users(self):
         """
@@ -745,7 +745,7 @@ class TestPasswordReset(TestCase, WagtailTestUtils):
         from django.utils.http import urlsafe_base64_encode
 
         # Get user
-        self.user = get_user_model().objects.get(username='test')
+        self.user = get_user_model().objects.get(email='test@email.com')
 
         # Generate a password reset token
         self.password_reset_token = PasswordResetTokenGenerator().make_token(self.user)
@@ -818,7 +818,7 @@ class TestPasswordReset(TestCase, WagtailTestUtils):
         self.assertRedirects(response, reverse('wagtailadmin_password_reset_complete'))
 
         # Check that the password was changed
-        self.assertTrue(get_user_model().objects.get(username='test').check_password('newpassword'))
+        self.assertTrue(get_user_model().objects.get(email='test@email.com').check_password('newpassword'))
 
     def test_password_reset_confirm_view_post_password_mismatch(self):
         """
@@ -846,7 +846,7 @@ class TestPasswordReset(TestCase, WagtailTestUtils):
             self.assertTrue("The two password fields didn't match." in response.context['form'].errors['new_password2'])
 
         # Check that the password was not changed
-        self.assertTrue(get_user_model().objects.get(username='test').check_password('password'))
+        self.assertTrue(get_user_model().objects.get(email='test@email.com').check_password('password'))
 
     def test_password_reset_done_view(self):
         """
@@ -872,7 +872,7 @@ class TestPasswordReset(TestCase, WagtailTestUtils):
 
     def test_password_reset_sensitive_post_parameters(self):
         request = RequestFactory().post('wagtailadmin_password_reset_confirm', data={})
-        request.user = get_user_model().objects.get(username='test')
+        request.user = get_user_model().objects.get(email='test@email.com')
         change_password(request)
         self.assertTrue(hasattr(request, 'sensitive_post_parameters'))
         self.assertEqual(request.sensitive_post_parameters, '__ALL__')
diff --git a/wagtail/admin/tests/test_filters.py b/wagtail/admin/tests/test_filters.py
index fba956753e..157041f930 100644
--- a/wagtail/admin/tests/test_filters.py
+++ b/wagtail/admin/tests/test_filters.py
@@ -34,7 +34,7 @@ class TestFilteredModelChoiceField(TestCase, WagtailTestUtils):
 
         class UserForm(forms.Form):
             users = FilteredModelChoiceField(
-                queryset=User.objects.order_by('username'), filter_field='id_group', filter_accessor='groups'
+                queryset=User.objects.order_by(User.USERNAME_FIELD), filter_field='id_group', filter_accessor='groups'
             )
 
         form = UserForm()
@@ -42,13 +42,15 @@ class TestFilteredModelChoiceField(TestCase, WagtailTestUtils):
         expected_html = """
             <select name="users" data-widget="filtered-select" data-filter-field="id_group" required id="id_users">
                 <option value="" selected>---------</option>
-                <option value="%(david)s" data-filter-value="%(musicians)s,%(actors)s">david</option>
-                <option value="%(kevin)s" data-filter-value="%(actors)s">kevin</option>
-                <option value="%(morten)s" data-filter-value="%(musicians)s">morten</option>
+                <option value="%(david)s" data-filter-value="%(musicians)s,%(actors)s">%(david_username)s</option>
+                <option value="%(kevin)s" data-filter-value="%(actors)s">%(kevin_username)s</option>
+                <option value="%(morten)s" data-filter-value="%(musicians)s">%(morten_username)s</option>
             </select>
         """ % {
             'david': self.david.pk, 'kevin': self.kevin.pk, 'morten': self.morten.pk,
             'musicians': self.musicians.pk, 'actors': self.actors.pk,
+            'david_username': self.david.get_username(), 'kevin_username': self.kevin.get_username(),
+            'morten_username': self.morten.get_username(),
         }
         self.assertHTMLEqual(html, expected_html)
 
@@ -56,7 +58,7 @@ class TestFilteredModelChoiceField(TestCase, WagtailTestUtils):
 
         class UserForm(forms.Form):
             users = FilteredModelChoiceField(
-                queryset=User.objects.order_by('username'), filter_field='id_group',
+                queryset=User.objects.order_by(User.USERNAME_FIELD), filter_field='id_group',
                 filter_accessor=lambda user: user.groups.all()
             )
 
@@ -65,12 +67,14 @@ class TestFilteredModelChoiceField(TestCase, WagtailTestUtils):
         expected_html = """
             <select name="users" data-widget="filtered-select" data-filter-field="id_group" required id="id_users">
                 <option value="" selected>---------</option>
-                <option value="%(david)s" data-filter-value="%(musicians)s,%(actors)s">david</option>
-                <option value="%(kevin)s" data-filter-value="%(actors)s">kevin</option>
-                <option value="%(morten)s" data-filter-value="%(musicians)s">morten</option>
+                <option value="%(david)s" data-filter-value="%(musicians)s,%(actors)s">%(david_username)s</option>
+                <option value="%(kevin)s" data-filter-value="%(actors)s">%(kevin_username)s</option>
+                <option value="%(morten)s" data-filter-value="%(musicians)s">%(morten_username)s</option>
             </select>
         """ % {
             'david': self.david.pk, 'kevin': self.kevin.pk, 'morten': self.morten.pk,
             'musicians': self.musicians.pk, 'actors': self.actors.pk,
+            'david_username': self.david.get_username(), 'kevin_username': self.kevin.get_username(),
+            'morten_username': self.morten.get_username(),
         }
         self.assertHTMLEqual(html, expected_html)
diff --git a/wagtail/admin/tests/test_page_chooser.py b/wagtail/admin/tests/test_page_chooser.py
index d631263e54..b7cae5b618 100644
--- a/wagtail/admin/tests/test_page_chooser.py
+++ b/wagtail/admin/tests/test_page_chooser.py
@@ -768,7 +768,7 @@ class TestCanChoosePage(TestCase, WagtailTestUtils):
     def test_with_user_no_permission(self):
         homepage = Page.objects.get(url_path='/home/')
         # event editor does not have permissions on homepage
-        event_editor = get_user_model().objects.get(username='eventeditor')
+        event_editor = get_user_model().objects.get(email='eventeditor@example.com')
         permission_proxy = UserPagePermissionsProxy(event_editor)
         result = can_choose_page(homepage, permission_proxy, self.desired_classes, user_perm='copy_to')
         self.assertFalse(result)