The correct answer is 4 in this case the tests are different. In the description you reach 1213, to reach 1214 you need a part of another year.

After solving (in my opinion) this puzzle, I get the same error from a test case of the "Attempt" submission.
I also think the correct answer for the test case :

p0: 1000
percent: 2.0
aug: 50
p: 1214

is 3, for 3 years.

This test case is similar to the one given in the kata's description and this description itself proposes 3 as the correct anwser. I completely agree with the demonstration of @uslu.

I don't understand how this is supposed to work. I convert the calculated population to an integer, but still get the number of years 3

A similar case is explained in the kata's description. Read it again.

At the end of the 2nd year there will be: 
1070 + 1070 * 0.02 + 50 => 1141 inhabitants (** number of inhabitants is an integer **)

careful, there are exceptions to the rules. It's in the link too

Where are you seeing the wrong order (sample tests, attempt tests)? In which language?

No, read the link.