This module provides code coverage metrics for Perl. Code coverage metrics describe how thoroughly tests exercise code. By using Devel::Cover you can discover areas of code not exercised by your tests and determine which tests to create to increase coverage. Code coverage can be considered an indirect measure of quality.

Devel::Cover is now quite stable and provides many of the features to be expected in a useful coverage tool.

Statement, branch, condition, subroutine, and pod coverage information is reported. Statement and subroutine coverage data should be accurate. Branch and condition coverage data should be mostly accurate too, although not always what one might initially expect. Pod coverage comes from Pod::Coverage. If Pod::Coverage::CountParents is available it will be used instead.

The cover program can be used to generate coverage reports. Devel::Cover ships with a number of reports including various types of HTML output, textual reports, a report to display missing coverage in the same format as compilation errors and a report to display coverage information within the Vim editor.

It is possible to add annotations to reports, for example you can add a column to an HTML report showing who last changed a line, as determined by git blame. Some annotation modules are shipped with Devel::Cover and you can easily create your own.

The gcov2perl program can be used to convert gcov files to Devel::Cover databases. This allows you to display your C or XS code coverage together with your Perl coverage, or to use any of the Devel::Cover reports to display your C coverage data.

Code coverage data are collected by replacing perl ops with functions which count how many times the ops are executed. These data are then mapped back to reality using the B compiler modules. There is also a statement profiling facility which should not be relied on. For proper profiling use Devel::NYTProf. Previous versions of Devel::Cover collected coverage data by replacing perl's runops function. It is still possible to switch to that mode of operation, but this now gets little testing and will probably be removed soon. You probably don't care about any of this.

The most appropriate mailing list on which to discuss this module would be perl-qa.

The Devel::Cover repository can be found on github. This is also where problems should be reported.

To get coverage for an uninstalled module:

cover -test

or

cover -delete
HARNESS_PERL_SWITCHES=-MDevel::Cover make test
cover

To get coverage for an uninstalled module which uses Module::Build (0.26 or later):

./Build testcover

If the module does not use the t/*.t framework:

PERL5OPT=-MDevel::Cover make test

If you want to get coverage for a program:

perl -MDevel::Cover yourprog args
cover

To alter default values:

perl -MDevel::Cover=-db,cover_db,-coverage,statement,time yourprog args