perlquestion
Wally Hartshorn
<p>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 <b>how</b> to do it. Nearly all of the programming I do involves database and CGI stuff.</p>
<p>Most of the information I've found about Test::Harness, Test::Simple, Test::More, etc, seem to focus on examples like this:</p>
<code>
is ( add_numbers(2, 2), 4);
is ( get_initials("John F. Kennedy"), "JFK");
</code>
<p>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:</p>
<ol>
<li>Retrieves data from a web form (via CGI.pm).</li>
<li>Retrieves the corresponding row from the database.</li>
<li>Fills in the template (via HTML::Template).
<li>Returns the HTML output (for display by CGI::Application).</li>
</ol></p>
<p>My suspicion is that I need to modify my program to make testing easier.</p>
<readmore>
<p>Suppose the original code is like this:</p>
<code>
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;
}
</code>
<p>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.</p>
<p>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 <b>data</b> ready for display, then test <b>that</b> routine instead. In other words, something more like this:
<code>
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;
}
</code>
<p>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().</p>
<p>Does that sound like Doing The Right Thing, or is there some nifty trick out there that I'm missing?</p>
<p>Wally Hartshorn<br><br>
(Plug: Visit [http://javajunkies.org/|JavaJunkies], PerlMonks for Java)</p>