Problem 381. Angle between two vectors

It would be good to have a more challenging test suite - see the guidelines for problems. Some solvers write code that is just a lookup table for the test cases, and having only one case makes it trivial to do this.

Also, your test should not use string comparison to evaluate what is a purely numerical computation. It would be better if you subtracted the correct answer from the proposed answer, and then compared the absolute value to a am all threshold, such as 1e-6.

Thnaks for your comments. It was my first or second problem sent to CODY. I didn't catch all the tricks to make strong test cases yet.