TDD is a lot like microservice adoption. If you start your project planning on a microservice architecture it is relatively simple to design it properly. If yo

TDD is a lot like microservice adoption. If you start your project planning on a microservice architecture it is relatively simple to design it properly. If your are migrating your monolithic application to microservices you are probably going to have a hard time. TDD is similar. If you start the project planning on writing your application TDD style it will be simpler. Converting your large business critical, not written to be tested, application over to TDD is not impossible but it makes business sense to "ship it" and hope for the best. Hiring a QA engineer would probably be less expensive than your developers rewriting your application to be "testable".