I've reduced the code a bit further (below) and ran the following two scenarios

First, I increased the number of temporary files being created in the test from 2 to 5. The function, which is otherwise unchanged, now fails every time. A print to the screen of the two arrays shows that they have the same content but in a different order.

In the second scenario, I amended the function so that the "expected" array is now passed in as a reference and then returned unchanged. The test which compares the expected array with the actual array then passes every time as expected. A print to the screen of the two arrays shows that they have the same content in the same order as would be expected.

It appears as though is_deeply is failing the test in the first scenario because of the array order.

Any thoughts? Thanks

Amended test code

note "\nTest function: get_files_in_watched_directory";
subtest 'get_files_in_watched_directory' => sub {
  my @got_files;
  my @expected_files;
  my $project_name = 'default';

  # create a temporary directory  
  my $temp_dir = tempdir( CLEANUP => 1 );

  # create some temporary files in the directory 
  my ($temp_file1_handle, $temp_file1)  = tempfile(DIR => $temp_dir);
  my ($temp_file2_handle, $temp_file2)  = tempfile(DIR => $temp_dir);
  my ($temp_file3_handle, $temp_file3)  = tempfile(DIR => $temp_dir);
  my ($temp_file4_handle, $temp_file4)  = tempfile(DIR => $temp_dir);
  my ($temp_file5_handle, $temp_file5)  = tempfile(DIR => $temp_dir);
  
  # create an array populated with the names of the temporary files th
+at we expectd to see
  push (@expected_files, basename($temp_file1));
  push (@expected_files, basename($temp_file2));
  push (@expected_files, basename($temp_file3));
  push (@expected_files, basename($temp_file4));
  push (@expected_files, basename($temp_file5));
  
  # now pass the temporary directory to the the function
  # the function should return an array @got_files with the names of t
+he files in the directory 
  @got_files = get_files_in_watched_directory($temp_dir, $project_name
+, \@expected_files);
  
  print "\n\nGOT\n";
  print Dumper(@got_files);
  print "\n";

  print "\n\nEXPECTED\n";
  print Dumper(@expected_files);
  print "\n";
  
  #compare the two arrays
  is_deeply(\@got_files, \@expected_files, 'Function should return a l
+ist of directory contents that will be processed');

};
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Amemded script under test

######################################################################
+##################################
sub get_files_in_watched_directory {  
  my ($directory_to_check, $project_name, $original_content_ref) = @_;
  my @problem_files;
  my @content_to_process;
  my $this_file;

  print "\n\nCalled Function: get_files_in_watched_directory";
  print "\n  Checking $directory_to_check";

  chdir ($directory_to_check) || die "cannot chdir to directory $direc
+tory_to_check: $!";
 
  # Get everything - files and directories - and decide what to do wit
+h each one
  opendir(DIR,$directory_to_check) || die "cannot open directory $dire
+ctory_to_check: $!";
  while (defined($this_file = readdir(DIR))) {  
      
    my $full_file_name = $directory_to_check . '/' . $this_file;

     # ignore the special directories "." and '.."
    if ($this_file =~ /^\.\.?$/) {
      next 
    }


    # wite anything else (file or directory) to an array to be process
+ed later
    else {
      print "\n    found: $this_file";
      push (@content_to_process, $this_file)
    }
  }
  closedir(DIR);
 
  print "\n\nabout to retun";
  
  #return @content_to_process;
  return (@{$original_content_ref});
}
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