Okay, I think it would be better to say "works for 30 minutes and then takes a 30-minute break".

"Works for 1 hour" could be taken to mean that they work for one hour before taking a break.

5 hours for all trees, our Junior team work 30min = 5 * 60 / 30 = 10 hours

Additionally, in case we receive an incorrect description of the garden, we need to handle the error:

It's unclear how we should handle the error; it's not mentioned, and the sample tests doesn't demonstrate this.

Could you explain how the math works on this example?

Junior - works for 1 hour with a 30-minute break.

howManyHours('(-{-(-', 'Junior') - result: '10 hour'

Two oaks and one birch take 5 hours to cut down. With a 30-minute break every hour, it takes 7.5 hours. Which rounds up to 8 hours. Why is the result 10 hours?

You don't generate error test cases in random tests. Either include these or get rid of incorrect gardens altogether.

solved this problem

Thanks for the answer, how could I make them? Or do you propose to increase the number of tests?

You need random tests

Well well, not mine kata)