Unit testing is a practice of writing code tests. TDD is the practice of writing them “before”. BDD is the practice of writing behavior/spec driven tests. Can I write BDD “after” or do I have to do it always “before”?
If you write BDD “after”, and it’s not BDD, then what it is called?
By definition of Behaviour Driven Development, you cannot write the behaviour tests after the code, however that does not mean that doing so isn’t useful. You may get more benefit from writing the spec tests first, but they are still useful as regression system tests for your application. So while you’re technically not practicing BDD, writing these tests is a good idea. One of the big perks of BDD is that it guides the development of the particular behaviour, so you are losing a lot of value by adding them later, but they still serve some use.
This is the same as writing unit tests after the code in TDD. It’s technically not TDD, but having the tests is obviously still useful.