There are various levels of testing, at an early stage you can write only integration and functional tests, later on when you get time you can write unit tests as well
If you don't unit test from day 1 then there's a strong probability that you wont be writing your code in a way that you can unit test later. e.g. mockable dependencies. I'm included to say go with TDD right from the start.
AndrewSChapman|6 years ago