Can some one please explain the problem

• Tests call sol twice per test case, which is unnecessary.
• Tests use the variable harmony after it was potentially mutated by user solution, what can lead to confusing messages or tests working incorrectly.
• Tests should not print to stdout if not necessary. Information usually looks better when presented with test headers, with custom assertion messages, if the message is expected to be short.
• Suggestion: return values of "Passed"/"Failed" scream for boolean and not strings.
• Question: your tests seem to generate test cases as failing or passing upfront. Is it even necessary to call the reference solution?

I'm new to this, I've been trying it for a while and have no idea (I didn't even know I could use _ as a variable).

I don't wanna look at the solutions, anything that could lead me to solve it?

Your control should be on solution not on the user's function only.

No random tests - see Kata authoring guidelines