yea

This is really cool.

Thank you. It's my first kata ever

It is clear that negative should take precedence but yes, it should be made more clear.

The test cases check for "Sound fair" but the kata description specifies "Sounds fair"

Also, what if the number is both odd and negative? One of those conditions should take precedence but this is left unspecified.

Edited.

Lots of typos. Description should read:

Just read that 4,153,237 people got married last year. Not to cause any trouble but shouldn't that be an even number?

Let's carefully check the number of people that got married last year. 
If it's an odd number, return "Not to cause any trouble but shouldn't that be an even number?"
If it's a negative number, return "Not to cause any trouble but shouldn't that be a positive number?"
If it's even and non-negative, return "Sounds fair"

Lacks random tests.

Validating values is not a novel idea.