Best practice for repository injection symfony in phpunit test class

I'm working with Symfony5, phpunit and api platform.

I'm trying to implement tests to make sur the API is secure.

I've created a class named TestContext that extand ApiTestCase and I make all my tests classes extands TestContext to reuse simply the methods I'll use in all my tests.

Now I'm also trying to inject repository on this class level, so I can access them in all the chlidren classes.

What would be the cleanest way to do that ?