Hi, thank you so much for your advices :)

• needs fixed tests in the test cases part too - i'm sorry but i don't know what you mean with this, can you explain better?
• make your method private, in the test class - fixed it
• increase the number of random tests - did it
• your random tests don't generate strings with numbers and moreover - i created a method that generates strings also with numbers

fixed it, that row 4 column 2 was a whitespace not a comma