def to_ftp(self, output_path, file_name, host, username, password):
    """Upload file to FTP server."""

    ftp = ftplib.FTP(host)
    ftp.login(username, password)
    full_path = os.path.join(output_path, file_name)
    with open(full_path, "r") as ftp_file:
        ftp.storbinary(" ".join(["STOR", file_name]), ftp_file.read)

@patch("ppc_model.io.ftplib.FTP")
def test_store_call(self, mock_ftp):
    """The *storbinary* call must use the right arguments."""

    with patch("ppc_model.io.open", mock_open(read_data=None)) as m:
        self.writer.to_ftp(output_path="./output", file_name="output.zip",
                       host="myftp", username="username", password="password")
    mock_ftp.return_value.storbinary.assert_called_once_with(
    "STOR output.zip", m.read())