Issue #3292980 by benjifisher, mikelutz, quietone: Testing system should...

              /** @var \Psr\Http\Message\StreamInterface $stream */

              $stream = $response->getBody();

              // Get the response body as a string.

              // Get the response body as a string. The response stream is set

              // to the sink, which defaults to a readable temp stream but can

              // be overridden by setting $options['sink'].

              $body = $stream->isReadable()

                ? (string) $stream

                : 'Response is not readable.';