The thing is the way they motivate new students to learn programming is by having them write programs that do something. Making a test green isn't as motivating as visually seeing the output of your work, and test fixtures can be complex to set up depending on the language. I mean students don't learn how to factor their code into methods until later into such a course, they're learning if statements and for loops and basic programming constructs. Don't you think having to explain setting up test fixtures and dependency inversion is a bit too much for people at that level?