tests/TestCase.php in a package?

I was wondering if there was a way to (composer) require the file tests/TestCase.php from in the GIT repo.

I would need this class to run tests for a yii2 extension I created. I basically required yii2 in my composer.json such as

"require": {

    "yiisoft/yii2": "*"


And tried to run my tests with

cd /my/package/location

composer update

./vendor/bin/phpunit ./tests

I get an error since yiiunit\TestCase class is missing

Fatal error: Class 'yiiunit\TestCase' not found

It is legit to expect my extension’s tests to run standalone? Should I implement my own TestCase class?