Challenge 2: Test a Subroutine From Course 1 — Possible Solution
====================================================================

# t/power.t
use strict;
use warnings;
use Test::More;

sub power {
    my ($base, $exponent) = @_;
    $exponent //= 2;
    return $base ** $exponent;
}

is(power(5), 25, 'power(5) defaults to squaring');
is(power(2, 8), 256, 'power(2, 8) uses explicit exponent');
is(power(3, 3), 27, 'power(3, 3) cubes correctly');

done_testing();

Running "prove t/power.t":
t/power.t .. ok
All tests successful.

WHY THIS WORKS AS AN ANSWER
------------------------------
The power subroutine is reused entirely unchanged from Course 1,
Chapter 7's own challenge solution — the //= defined-or default for
$exponent and the ** exponentiation operator both work exactly as
originally written; the only new thing here is testing it.

is(power(5), 25, ...) reuses this chapter's own is() pattern to
verify the DEFAULT-exponent path specifically — calling power with
only one argument should fall back to squaring, and 5 ** 2 = 25
confirms that.

is(power(2, 8), 256, ...) and is(power(3, 3), 27, ...) both test the
EXPLICIT-exponent path with two different inputs — 2 ** 8 = 256 and
3 ** 3 = 27 — deliberately covering both branches of the subroutine's
actual behavior (default vs. explicit) rather than just one, which is
what makes this a genuinely useful test rather than a single
coincidental check.

done_testing(); reuses the chapter's own modern-style closing call,
and running prove t/power.t against the file confirms all three
assertions pass, verifying power() behaves correctly across its full
range of intended use.