How can i test a recursive function in Kotlin?

Im trying to test the following function:

    private tailrec fun findFixPoint(eps: Double = 5.0, x: Double = 1.0): Double = if (abs(x - cos(x)) < eps) x else findFixPoint(cos(x))

This is my test function:

@Test
fun testNewFeatures(){
    TestCase.assertEquals(0.7390851332151611, findFixPoint())
}

The fix point is 0.7390851332151611 but the assertEquals returns me 1.0 as Actualvalue i can deduct the function is only being launch one time without recursion.

Any suggestion of how can be test a tailrec function properly?

Hope anyone can help me with this. Thank you all in advance.