Suppose the original code is like this:

sub show_record {
    my $self = shift;
    my $cgi = $self->query();
    my $emp_no = $cgi->param("emp_no");
    ...
    # code to access the database omitted
    ...
    my $emp_rec = $sth->fetchrow_hashref;
    ...
    # code to fiddle with the data omitted
    ...
    my $template = $self->load_tmpl(emp_detail.tmpl.html');
    $template->param( $emp_rec );
    return $template->output;
}
[download]

As it is now, I can't figure out how to write a test that would verify that the web page displayed for employee number "12345" is correct. How would I cause $cgi->param("emp_no") to return "12345"? How would I compare the web page to the expected value? When someone changes the format of the web page, the test would break. Etc.

As I thought about it, I realized that testing for the value of the web page would not be Doing The Right Thing. Instead, I should probably have a subroutine that gets the data ready for display, then test that routine instead. In other words, something more like this:

sub show_record {
    my $self = shift;
    my $cgi = $self->query();
    my $emp_no = $cgi->param("emp_no");

    my $emp_rec = get_emp_data($emp_no);

    my $template = $self->load_tmpl(emp_detail.tmpl.html');
    $template->param( $emp_rec );
    return $template->output;
}

sub get_emp_data {
    my ($emp_no) = (@_);
    ...
    # code to access the database omitted
    ...
    my $emp_rec = $sth->fetchrow_hashref;
    ...
    # code to fiddle with the data omitted
    ...
    return $emp_rec;
}
[download]

With the above changes, I wouldn't do unit tests of show_record(), on the theory that it is pretty much all presentation code, not logic (although if anyone has suggestions on how to write unit tests for that, I'm interested). Instead, I would just test get_emp_rec().

Does that sound like Doing The Right Thing, or is there some nifty trick out there that I'm missing?

Wally Hartshorn

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