Unit Testing CGI Programs

[Wally Hartshorn]

I'm attempting to Do The Right Thing (tm), i.e. unit test my programs. I've been reading about unit testing, and it sounds like a very good idea -- I'm sold on the concept! Unfortunately, I've been having problems figuring out how to do it. Nearly all of the programming I do involves database and CGI stuff.

Most of the information I've found about Test::Harness, Test::Simple, Test::More, etc, seem to focus on examples like this:

is ( add_numbers(2, 2), 4);
is ( get_initials("John F. Kennedy"), "JFK");

I can understand how to write that kind of test, but I'm having trouble figuring out how to write a test for code that:

1. Retrieves data from a web form (via CGI.pm).
2. Retrieves the corresponding row from the database.
3. Fills in the template (via HTML::Template).
4. Returns the HTML output (for display by CGI::Application).

My suspicion is that I need to modify my program to make testing easier.

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;
}

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;
}

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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