Fixes location of temporary file created in tests (#9403)

Solves small Issue created in a60f589

The file was created in the sources 'file' when run from IDE which
might be accidentally committed. This change prevents it.

tests/providers/amazon/aws/transfers/test_mysql_to_s3.py

@@ -17,6 +17,7 @@
 # under the License.
 #
 import unittest
+from tempfile import NamedTemporaryFile
 from unittest import mock
 
 import pandas as pd
@@ -33,29 +34,29 @@ def test_execute(self, mock_mysql_hook, mock_s3_hook, temp_mock):
         query = "query"
         s3_bucket = "bucket"
         s3_key = "key"
-        filename = "file"
 
         test_df = pd.DataFrame({'a': '1', 'b': '2'}, index=[0, 1])
         get_pandas_df_mock = mock_mysql_hook.return_value.get_pandas_df
         get_pandas_df_mock.return_value = test_df
-        temp_mock.return_value.__enter__.return_value.name = filename
-
-        op = MySQLToS3Operator(query=query,
-                               s3_bucket=s3_bucket,
-                               s3_key=s3_key,
-                               mysql_conn_id="mysql_conn_id",
-                               aws_conn_id="aws_conn_id",
-                               task_id="task_id",
-                               pd_csv_kwargs={'index': False, 'header': False},
-                               dag=None
-                               )
-        op.execute(None)
-        mock_mysql_hook.assert_called_once_with(mysql_conn_id="mysql_conn_id")
-        mock_s3_hook.assert_called_once_with(aws_conn_id="aws_conn_id", verify=None)
-
-        get_pandas_df_mock.assert_called_once_with(query)
-
-        temp_mock.assert_called_once_with(mode='r+', suffix=".csv")
-        mock_s3_hook.return_value.load_file.assert_called_once_with(filename=filename,
-                                                                    key=s3_key,
-                                                                    bucket_name=s3_bucket)
+        with NamedTemporaryFile() as f:
+            temp_mock.return_value.__enter__.return_value.name = f.name
+
+            op = MySQLToS3Operator(query=query,
+                                   s3_bucket=s3_bucket,
+                                   s3_key=s3_key,
+                                   mysql_conn_id="mysql_conn_id",
+                                   aws_conn_id="aws_conn_id",
+                                   task_id="task_id",
+                                   pd_csv_kwargs={'index': False, 'header': False},
+                                   dag=None
+                                   )
+            op.execute(None)
+            mock_mysql_hook.assert_called_once_with(mysql_conn_id="mysql_conn_id")
+            mock_s3_hook.assert_called_once_with(aws_conn_id="aws_conn_id", verify=None)
+
+            get_pandas_df_mock.assert_called_once_with(query)
+
+            temp_mock.assert_called_once_with(mode='r+', suffix=".csv")
+            mock_s3_hook.return_value.load_file.assert_called_once_with(filename=f.name,
+                                                                        key=s3_key,
+                                                                        bucket_name=s3_bucket)