Unit testing à Developers test each module or block of code during development.
• Component Testing à Component is a standalone functionality that can work 
by itself. Ex. Amazon Buyer Functionality,
Seller Functionality, Prime Video Functionality.
• Integration Testing à Combine all of the Functionalities. 
When I integrate them, can I still use all of the functions? Make
sure they all still work.
• System Testing à End-to-End testing. Test everything from beginning to end.
• Acceptance Testing à Hire a UAT (User Acceptance Testing) Team or
Business Analyst can also do Acceptance Testing.
After testing has been complete you have to get another team to do 
acceptance testing so they can confirm the QA teams
testing was successful and have the product ready for the customer