I recently had the opportunity to instruct several new developers in the nuances of the Ruby language.
There is a strong emphasis now for developers to test drive their development. Several of the exercises utilized tests as a safety net. Other exercises did have them write code to make tests pass.
Despite what I would call a solid upbringing the students do not immediately reach for their test framework when they start working on new exercises. It just does not feel comfortable trying to write tests when you barely have an understanding of the complexity of the problem and the scope of the language.
To those of us polyglots, now working in our third or fourth language we find it a far easier venture. I think we should think twice before we require, enforce, or guilt new developers writing software to bring with them tests in tow.
Test Driven Development requires a much greater level of mastery and understanding than we often give credit.