def METHOD_NAME(self, mock_db):
    conn = mock.MagicMock()
    mock_db.return_value.__enter__.return_value = conn
    with conn.cursor() as cursor:
        cursor.execute.return_value.fetchall.return_value = []
        results = get_browser_sample_lists(species_id="12")
        self.assertEqual(results, {"mouse": [], "rat": []})