The document discusses automating unit tests for legacy code. It presents examples of testing a Users module that retrieves user data from a database. The examples show adding stubs and mocks to isolate the code from its dependencies, and testing different code paths like when a user is found, not found, and deleted from the database. The document suggests automating tests in this way allows legacy code to be refactored more easily while preserving existing functionality through the tests.

1. Unit tests automation for legacy code
Denis Shirokov
Rexuni.com
YAPC::NA 2016

2. Simple situation
package Users;
use strict;
use warnings;
use DB;
sub get {
my ($user_id) = @_;
my $user = DB::fetch_query( "SELECT * FROM users WHERE id = ?", $user_id );
if ($user) {
return $user;
} else {
die('no user found');
}
}
1;

3. Subroutine execution
use Users;
use Data::Dumper;
print Dumper Users::get(1);

4. Test for simple situation
sub fetch_exists : Auto {
my ($self) = @_;
$self->addStub('DB::fetch_query');
my $result = Users::get(1);
$self->setResult($result);
}

5. Record/Play mode
sub get {
my ($user_id) = @_;
my $user = DB::fetch_query( "SELECT * FROM users WHERE id = ?", $user_id );
if ($user) {
return $user;
} else {
die('no user found');
}
}

6. Database change
package Users;
use strict;
use warnings;
use DB;
sub get {
my ($user_id) = @_;
my $user = DB::fetch_query( "SELECT * FROM users WHERE id = ?", $user_id );
if ($user) {
return $user;
} else {
die('no user found');
}
}
1;

7. Update mode

9. Exception example
sub fetch_not_exists : Auto {
my ($self) = @_;
$self->addStub('DB::fetch_query');
my $result = Users::get(-42);
return $self->setResult($result);
}

11. Ensure function call
package Users;
...
sub delete {
my ($user_id) = @_;
DB::query( "DELETE FROM users WHERE id = ?", $user_id );
return 1;
}

12. Test for user deletion
sub delete_user : Auto {
my ($self) = @_;
$self->addMock('DB::query');
my $result = Users::delete(1);
$self->setResult($result);
}

13. Questions?

14. Thank you
Denis
ShirokovRexuni.com