My function is not called a second time why [duplicate]

Here is my code for my simple function, below when I use echo and my function with a number greater than zero, the function returns true(1), when the number is less than zero, nothing happens, the code and the output of the program are attached

<?php
  function isPositive(int $number) : bool{
        return $number > 0;
    }

    echo "testn";
    echo isPositive(1);
    echo "testn";
    echo isPositive(-1);
    echo "testn";

output

I expected the is Positive(-1) function to return false (0)