Error: Class PHPUnit\Framework\TestCase not found and could not be autoloaded

[txemapamundi9l]

Hello, I don't think this is a bug, but am hoping someone might be able to help me solve the problem, which other people might have.

I installed Drupal using Composer and drupal/recommended-project. When I run drupal-check on a module directory, I get the following error:
Class PHPUnit\Framework\TestCase not found and could not be autoloaded

How can you remove this error? It looks like PHPUnit is not included with drupal/recommended-project. The instructions at the following page just say to do 'composer install' or 'composer update', but I did that and still no PHPUnit:
https://www.drupal.org/docs/8/phpunit/running-phpunit-tests

[arderyp]

I get similar errors:

Class Drupal\Tests\UnitTestCase not found and could not be autoloaded.
Class Drupal\KernelTests\KernelTestBase not found and could not be autoloaded.
Class Drupal\Tests\BrowserTestBase not found and could not be autoloaded.
## and many more related to the module ##

Executing against some specific modules works fine, but executing against others doesn't (ctools and page_manager, to name two)

[ytsurk]

drupal/core-dev to the resque 🗡️

See: https://drupal.stackexchange.com/a/293684

Basically when working on D8.9, use:

composer require --dev --with-all-dependencies 'drupal/core-dev:^8.9'