Why don't just learn algorithms and other computer science "direct" approach by analysing problem and solving it in most officiant way? This doesn't really say

Why don't just learn algorithms and other computer science "direct" approach by analysing problem and solving it in most officiant way? This doesn't really say anything; your statement amounts to "Why not do it properly, instead of using tests?" - it should be obvious why that's invalid. In particular, unit testing protects against "minor changes with unexpected consequences." This happens all of the time. "analysing problem and solving it" will not make a bit of difference. Do you expect that people who use unit tests are instead "ignoring the problem and not solving it?" A test ratio of 2:1 isn't a big deal. It serves as a record: "Here's a specification of what my code does. You can automatically verify that it does what it says." Think of it as part spec, part test.