Go check out the example they give in the instructions that's similar to this test except for the desired population (1200 in example, 1214 in test). Notice they don't return a float for their population after every year of growth.

good point, I guess (on your side only x) )

(edit: oops, that ofc was a "once" in my previous message)

I guess that's a cheap way of making it unique?

what's the point of the restrictions? You're enforcing the use of rather "raw" stuff (see Steffan's solution) that nobody wants to use ones they know about more evoluated syntaxes => I'm really wondering about the point behind the kata?

Ruby naming conventionn is snake_case, not camelCase

Needs random tests.

Not an issue, read this again:

1070 + 1070 * 0.02 + 50 => 1141 inhabitants (number of inhabitants is an integer)

You're working with floats there.

The seventh basic test should be 3, but it is expecting to be 4.

Test params:
p0=1000
percent=2.0
aug=50
p=1214

Here are my logs:
1 years, p=1070.0
2 years, p=1141.4
3 years, p=1214.228