[s3] fix S3Boto3StorageFile.closed (#1249)

storages/backends/s3boto3.py

@@ -132,6 +132,10 @@ def __init__(self, name, mode, storage, buffer_size=None):
     def size(self):
         return self.obj.content_length
 
+    @property
+    def closed(self):
+        return not self._file or self._file.closed
+
     def _get_file(self):
         if self._file is None:
             self._file = SpooledTemporaryFile(

tests/test_s3boto3.py

@@ -787,3 +787,24 @@ def test_querystring_auth(self):
 
     def test_save(self):
         self.storage.save('x.txt', ContentFile(b'abc'))
+
+
+class S3Boto3StorageFileTests(TestCase):
+    def setUp(self) -> None:
+        self.storage = s3boto3.S3Boto3Storage()
+        self.storage._connections.connection = mock.MagicMock()
+
+    def test_closed(self):
+        f = s3boto3.S3Boto3StorageFile('test', 'wb', self.storage)
+
+        with self.subTest("is True after init"):
+            self.assertTrue(f.closed)
+
+        with self.subTest("is False after file access"):
+            # Ensure _get_file has been called
+            f.file
+            self.assertFalse(f.closed)
+
+        with self.subTest("is True after close"):
+            f.close()
+            self.assertTrue(f.closed)