Cannot modify header information - headers already sent

[shynkaruck]

If i sent dispatchAction to controller and this controller has redirect to another link, test crash with error Cannot modify header information - headers already sent by (output started vendor/phpunit/phpunit/src/Util/Printer.php:134). For example ,create new product

[in2part]

Try to run phpunit with flag --stderr

For example:
vendor/bin/phpunit --testsuite catalog --stderr