As we talked about, there are 2 types of coding lessons on Boot.dev:
Console output lessons
Unit-test lessons
Console Output Lessons
Only 1 file of code, usually with a comment explaining where to write your code
When you "submit" your code, its console output must match the expected output exactly to pass
Debug print statements will cause your code to fail submission, so remove them before submitting
Unit-Test Lessons
2 files of code: main and main_test. You can read the tests but you can't edit them
When you "submit" your code, the return values of your functions must match the expected values exactly to pass
Console output is ignored, you can leave debug print statements in your code
Which Is More Common?
Going forward, you'll encounter far more unit-test lessons than console output lessons, but you'll still see both from time to time. Different concepts are better suited to different types of lessons.