Who all are the people/teams involved in different levels/phases of testing?

Once the coding phase is over, the application moves to Testing phase, this means that unit test of the application is already performed.

Let’s be ensured that unit testing of the application is performed by the developers, once unit testing is done, the application goes into the next phase which is

component testing, this testing is performed by testing team, after component testing the application gets in integration testing which is again conducted by testers and after integration testing sign off is given, system testing is performed by highly experienced domain expert quality analysts.

Now after system test is done, application goes for acceptance testing and this testing is done by the product owner.