Add test for TenantFileSystemStorage(), Refs django-tenants#249

according to documentation TenantFileSystemStorage() will create
a separate directory for each schema_name under MEDIA_ROOT.

This is not currently the case! My speculation is that this is
broken because the subdir prefix is configured only once in the
constructor of TenantFileSystemStorage() and then cached. Thus we
end-up using the schema_name of the first tenant which happens to
save files.

The fact that TenantFileSystemStorageTestCase.test_format_string
broke without changing anything else supports the above speculation.
The reason is that the new
test_files_are_saved_under_subdirectories_per_tenant() test method
is executed *before* test_format_string()!

django_tenants/tests/test_filesystem_storage.py

@@ -1,7 +1,10 @@
 import warnings
 
 from django.conf import settings
+from django.db import connection
+from django.core.files.base import ContentFile
 
+from django_tenants import utils
 from django_tenants.files.storage import TenantFileSystemStorage
 from django_tenants.files.storages import TenantFileSystemStorage as OldTenantFileSystemStorage
 from django_tenants.test.cases import TenantTestCase
@@ -68,3 +71,49 @@ def test_deprecated_module_raises_warning(self):
 
             OldTenantFileSystemStorage()
             self.assertTrue(any(deprecation_warning in str(w.message) for w in warns))
+
+    def test_files_are_saved_under_subdirectories_per_tenant(self):
+        storage = TenantFileSystemStorage()
+
+        connection.set_schema_to_public()
+        tenant1 = utils.get_tenant_model()(schema_name='tenant1')
+        tenant1.save()
+
+        domain1 = utils.get_tenant_domain_model()(tenant=tenant1, domain='something.test.com')
+        domain1.save()
+
+        connection.set_schema_to_public()
+        tenant2 = utils.get_tenant_model()(schema_name='tenant2')
+        tenant2.save()
+
+        domain2 = utils.get_tenant_domain_model()(tenant=tenant2, domain='example.com')
+        domain2.save()
+
+        # this file should be saved on the public schema
+        public_file_name = storage.save('hello_world.txt', ContentFile('Hello World'))
+        public_os_path = storage.path(public_file_name)
+
+        # switch to tenant1
+        with utils.tenant_context(tenant1):
+            t1_file_name = storage.save('hello_from_1.txt', ContentFile('Hello T1'))
+            t1_os_path = storage.path(t1_file_name)
+
+        # switch to tenant2
+        with utils.tenant_context(tenant2):
+            t2_file_name = storage.save('hello_from_2.txt', ContentFile('Hello T2'))
+            t2_os_path = storage.path(t2_file_name)
+
+        # assert the paths are correct
+        self.assertTrue(public_os_path.endswith('%s/public/%s' % (settings.MEDIA_ROOT, public_file_name)))
+        self.assertTrue(t1_os_path.endswith('%s/tenant1/%s' % (settings.MEDIA_ROOT, t1_file_name)))
+        self.assertTrue(t2_os_path.endswith('%s/tenant2/%s' % (settings.MEDIA_ROOT, t2_file_name)))
+
+        # assert contents are correct
+        with open(public_os_path, 'r') as f:
+            self.assertEqual(f.read(), 'Hello World')
+
+        with open(t1_os_path, 'r') as f:
+            self.assertEqual(f.read(), 'Hello T1')
+
+        with open(t2_os_path, 'r') as f:
+            self.assertEqual(f.read(), 'Hello T2')