Would throw an excpetion like following message

    PHPUnit\Framework\Exception: PHP Fatal error:  Allowed memory size of
    73400320 bytes exhausted (tried to allocate 31457312 bytes) in
    /home/gasolwu/Code/sabre-http/lib/Client.php on line 437

Let PHPUnit be quiet

    PHPUnit 7.5.1 by Sebastian Bergmann and contributors.

      Warning - The configuration file did not pass validation!
      The following problems have been detected:

      Line 8:
      - Element 'phpunit', attribute 'strict': The attribute 'strict' is not allowed.

      Test results may not be as expected.

See sebastianbergmann/phpunit@78c8865

The feature needs to install additional package.

    Error: Package phpunit/php-invoker is required for enforcing time limits

In order to resolve sabre-io#82 to avoid additional memory copy of response body
(from $response to $responseBody), We deperecated `parseCurlResult` method
which use `substr` function to separate HTTP headers and body and create new
method `parseCurlResponse` instead. We register `receiveCurlHeader` method
as callback function by curl_setopt using `CURLOPT_HEADERFUNCTION` option.

This changes is not intended to resolve issue sabre-io#15

See sabre-io#115 (comment)

Use local variable instead

Fix error like

    TypeError: Return value of Sabre\HTTP\Client::curlExec() must be of
    the type string, boolean returned