I have a sum.php file which has the following function:

# Adds two integers
function sum(
    int $a,
    int $b
): int 
{
    return $a + $b;
}

In the file SumTest.php, I’m testing sum() like this:

it('sums two integers', function () {
    $result = sum(1, 2);
    
    expect($result)->toBe(3);
});

After running ./vendor/bin/pest I get this result:

   FAIL  TestsUnitSumTest
  ⨯ it sums two integers                                                                                                                0.02s  
  ────────────────────────────────────────────────────────────────
   FAILED  TestsUnitSumTest > it sums two integers                                                                                   Error   
  Call to undefined function sum()

  at testsUnitSumTest.php:4
      1▕ <?php
      2▕
      3▕ it('sums two integers', function () {
  ➜   4▕     $result = sum(1, 2);
      5▕
      6▕     expect($result)->toBe(3);        
      7▕ });
      8▕

  1   testsUnitSumTest.php:4

Why isn’t it recognizing the sum() function?