This issue { Magento2 unit tests doesn’t run using vendor/bin/phpunit -c } is mainly getting solve by deleting vendor file and then firing composer install command but it is till exit then please use this command

“php -f ./vendor/phpunit/phpunit/phpunit -c dev/tests/unit/phpunit.xml ./app/code/Nilesh/UnitTest/Test/Unit/Model/UnitTestTest.php"

Please remember this is one command and to use PHP at the start of your command or else you will face permission issue.

And also u can see I have added -f flag too because some time XML file generated unexpected error which can be ignored.

For example: