How to fix this error Package phpunit/phpunit-mock-objects is abandoned, you should avoid using it. No replacement was suggested
PHPUnit version PHP Version composer
----------------- --------------- -------------------------
PHPUnit 8 PHP 7.2 / 7.3 "phpunit/phpunit": "^8"
PHPUnit 7 PHP 7.1 "phpunit/phpunit": "^7"
PHPUnit 6 PHP 7.0 "phpunit/phpunit": "^6"
PHPUnit 5 PHP 5.6 "phpunit/phpunit": "^5"
Note: PHP 7.1 is no longer actively supported.
See this link
composer: add --ignore-platform-reqs