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Devel::CoverX::Covered - Collect and report caller (test file) and covered (source file) statistics from the cover_db


Dealing with large code bases and large test suites

When a test suite grows as a team of developers implement new features, knowing exactly which test files provide test coverage for which parts of the application becomes less and less obvious.

This is especially true for tests on the acceptance / integration / system level (rather than on the unit level where the tests are more concentrated and easily deduced).

This is also extra difficult for developers new to the code base who have no clue what types of code may need extra testing, or about common idioms for testing certain parts of the application.

Enter Devel::CoverX::Covered

Devel::CoverX::Covered extracts and stores the relationship between covering test files and covered source files from a Devel::Cover cover_db.

This makes it possible to

  • Given a source file, list the test files that provide coverage to that source file. This can be done on a file, sub routine and row level.

  • Given a test file, list the source files and subs covered by that test file.

  • Given a source file, report efficiently on the coverage details per row, or sub.

Usage Scenarios

Using this module it should be possible to implement e.g.

  • From within the editor, list or open interesting source / test files, depending on the editor context (current file, sub, line).

  • When a source file is saved or changed on disk, look up which tests correspond to that source file and run only those, thereby providing a quicker feedback loop than running the entire test suite.

  • In the editor, highlight source code with code coverage details.

  • Determine how "unity" a unit test is. That is, how much of the code base does the unit test touch? A focused unit test would not reach too many parts of the source code.


The general output format is one record per line. When there are may columns per record, they are tab separated.

Development Status

Moderately mature, but incomplete feature-wise. Solid, but somewhat prone to change as a result of feedback.


Nightly / automatic run

  #Clean up from previous test run (optional)
  cover -delete

  #Test run with coverage instrumentation
  PERL5OPT=-MDevel::Cover prove -r t

  #Collect covered and caller information
  #  Run this _before_ running "cover"
  #  Don't run with Devel::Cover enabled
  covered runs
    - or e.g. -
  covered runs --rex_skip_test_file='/$/' \

  #Post process to generate covered database
  cover -report Html_basic  # Needs Template installed

During development

  #List version, and all known files
  covered info

  #Query the covered database per source file
  covered covering --source_file=lib/MyApp/

  #Query the covered database per source file and a specific sub
  covered covering --source_file=lib/MyApp/ --sub=get_odd_values

  #Query the covered database per test file
  covered by --test_file=t/myapp-do_stuff.t

  #Query the covered database for coverage details of a source file
  #sub_name \t coverage count (0 is red, >= 1 is green)
  covered subs --source_file=lib/MyApp/
  new       4
  as_string 32
  as_xml    0
  do_stuff  4

-- not implemented --

  #Query the covered database per source file and row
  covered covering --source_file=lib/MyApp/ --row=37

  covered covering --source_file=lib/MyApp/ --row=142

  #Query the covered database per test file, but also show covered
  #subroutines (\t separated)
  covered subs_by --test_file=t/myapp-do_stuff.t
  lib/MyApp/       as_xml
  lib/MyApp/       do_stuff
  lib/MyApp/       new
  lib/MyApp/DoStuff/   new
  lib/MyApp/DoStuff/   do_other_stuff

  #Query the covered database for details of a source file
  covered lines --source_file=lib/MyApp/ --metric=statement
  11   1
  17   0
  26   0
  32   1
  77   3
  80   1
  99   2
  102  2
  104  1


The Devel::CoverX::Covered database is the "covered" directory located next to the "cover_db" directory. It is created by running the "covered runs" command (see the SYNOPSIS above).



Devel::PerlySense has a feature "Go to Tests - Other Files" for navigating to related files. Limit the list of test files when point is on a "sub name" line.

PerlySense can also highlight subroutine coverage in the source code.


There is a vim plugin at, which provides functions for re-running tests covering the current subroutine, or if you are in a test file, re-run that testfile. It can also show files covering the current file, and what modules are covered by the current test file. It shows TAP output syntax highlighten in a seperate buffer that updates when you re-run the tests, making the feedback cycle (if your tests are quick) quite nice.

Ovid provides similar key bindings here:



Tests run by Test::Aggregate won't be reported properly. That's because the single .t file running all the aggregate tests will be reported as the covering test file.

The workaround is to perform the Devel::Cover test run without Test::Aggregate, i.e. do something like (assuming "aggtest" contains your aggregate tests):

  PERL5OPT=-MDevel::Cover prove -r t aggtest

The extra time taken to do this is probably not a problem since running tests with Devel::Cover enabled is so very slow anyway. The startup time is simply less significant here.

Another clear benefit is that it will result in smaller individual Devel::Cover run files, which may otherwise be too large to handle efficiently.




Johan Lindstrom, <johanl [AT]>



Please report any bugs or feature requests to, or through the web interface at I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


The Devel::Cover db version is hard coded since it's not exposed by Devel::Cover. So that's a bit fragile.


If you delete a .t file, running the test suite again won't de-register it from the covered database. To get rid of it you need to delete the "covered" directory and re-run the entire coverage test suite.


Copyright 2007 Johan Lindstrom, All Rights Reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.