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NAME
Devel::Cover - Code coverage metrics for Perl

VERSION
version 1.36

SYNOPSIS
To get coverage for an uninstalled module:

cover -test

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

DESCRIPTION
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.

Although it is still being developed, 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.
Coverage data for other criteria are not yet collected.

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. See
<http://lists.perl.org/list/perl-qa.html>.

The Devel::Cover repository can be found at <http://github.com/pjcj/Devel--Cover>. This is also
where problems should be reported.

REQUIREMENTS AND RECOMMENDED MODULES
REQUIREMENTS
* Perl 5.10.0 or greater.

The latest version of Devel::Cover on which Perl 5.8 was supported was 1.23. Perl versions
5.6.1 and 5.6.2 were not supported after version 1.22. Perl versions 5.6.0 and earlier were
never supported. Using Devel::Cover with Perl 5.8.7 was always problematic and frequently
lead to crashes.

Different versions of perl may give slightly different results due to changes in the op
tree.

* The ability to compile XS extensions.

This means a working C compiler and make program at least. If you built perl from source you
will have these already and they will be used automatically. If your perl was built in some
other way, for example you may have installed it using your Operating System's packaging
mechanism, you will need to ensure that the appropriate tools are installed.

* Storable and Digest::MD5

Both are in the core in Perl 5.8.0 and above.

REQUIRED MODULES
* B::Debug

This was core before Perl 5.30.0.

OPTIONAL MODULES
* Template, and either PPI::HTML or Perl::Tidy

Needed if you want syntax highlighted HTML reports.

* Pod::Coverage (0.06 or above) or Pod::Coverage::CountParents

One is needed if you want Pod coverage. If Pod::Coverage::CountParents is installed, it is
preferred.

* Test::More

Required if you want to run Devel::Cover's own tests.

* Test::Differences

Needed if the tests fail and you would like nice output telling you why.

* Template and Parallel::Iterator

Needed if you want to run cpancover.

* JSON::MaybeXS

JSON is used to store the coverage database if it is available. JSON::MaybeXS will select
the best JSON backend installed.

Use with mod_perl
By adding "use Devel::Cover;" to your mod_perl startup script, you should be able to collect
coverage information when running under mod_perl. You can also add any options you need at this
point. I would suggest adding this as early as possible in your startup script in order to
collect as much coverage information as possible.

Alternatively, add -MDevel::Cover to the parameters for mod_perl. In this example, Devel::Cover
will be operating in silent mode.

PerlSwitches -MDevel::Cover=-silent,1

OPTIONS
-blib - "use blib" and ignore files matching \bt/ (default true
if blib directory exists, false otherwise)
-coverage criterion - Turn on coverage for the specified criterion. Criteria
include statement, branch, condition, path, subroutine,
pod, time, all and none (default all available)
-db cover_db - Store results in coverage db (default ./cover_db)
-dir path - Directory in which coverage will be collected (default
cwd)
-ignore RE - Set regular expressions for files to ignore (default
"/Devel/Cover\b")
+ignore RE - Append to regular expressions of files to ignore
-inc path - Set prefixes of files to include (default @INC)
+inc path - Append to prefixes of files to include
-loose_perms val - Use loose permissions on all files and directories in
the coverage db so that code changing EUID can still
write coverage information (default off)
-merge val - Merge databases, for multiple test benches (default on)
-select RE - Set regular expressions of files to select (default none)
+select RE - Append to regular expressions of files to select
-silent val - Don't print informational messages (default off)
-subs_only val - Only cover code in subroutine bodies (default off)
-replace_ops val - Use op replacing rather than runops (default on)
-summary val - Print summary information if val is true (default on)

More on Coverage Options
You can specify options to some coverage criteria. At the moment only pod coverage takes any
options. These are the parameters which are passed into the Pod::Coverage constructor. The extra
options are separated by dashes, and you may specify as many as you wish. For example, to
specify that all subroutines containing xx are private, call Devel::Cover with the option
-coverage,pod-also_private-xx.

Or, to ignore all files in "t/lib" as well as files ending in "Foo.pm":

cover -test -silent -ignore ^t/lib/,Foo.pm$

Note that "-ignore" replaces any default ignore regexes. To preserve any ignore regexes which
have already been set, use "+ignore":

cover -test -silent +ignore ^t/lib/,Foo.pm$

SELECTING FILES TO COVER
You may select the files for which you want to collect coverage data using the select, ignore
and inc options. The system uses the following procedure to decide whether a file will be
included in coverage reports:

* If the file matches a RE given as a select option, it will be included

* Otherwise, if it matches a RE given as an ignore option, it won't be included

* Otherwise, if it is in one of the inc directories, it won't be included

* Otherwise, it will be included

You may add to the REs to select by using +select, or you may reset the selections using
-select. The same principle applies to the REs to ignore.

The inc directories are initially populated with the contents of perl's @INC array. You may
reset these directories using -inc, or add to them using +inc.

Although these options take regular expressions, you should not enclose the RE within // or any
other quoting characters.

The options -coverage, [+-]select, [+-]ignore and [+-]inc can be specified multiple times, but
they can also take multiple comma separated arguments. In any case you should not add a space
after the comma, unless you want the argument to start with that literal space.

UNCOVERABLE CRITERIA
Sometimes you have code which is uncoverable for some reason. Perhaps it is an else clause that
cannot be reached, or a check for an error condition that should never happen. You can tell
Devel::Cover that certain criteria are uncoverable and then they are not counted as errors when
they are not exercised. In fact, they are counted as errors if they are exercised.

This feature should only be used as something of a last resort. Ideally you would find some way
of exercising all your code. But if you have analysed your code and determined that you are not
going to be able to exercise it, it may be better to record that fact in some formal fashion and
stop Devel::Cover complaining about it, so that real problems are not lost in the noise.

If you have uncoverable criteria I suggest not using the default HTML report (with uses
html_minimal at the moment) because this sometimes shows uncoverable points as uncovered.
Instead, you should use the html_basic report for HTML output which should behave correctly in
this regard.

There are two ways to specify a construct as uncoverable, one invasive and one non-invasive.

Invasive specification
You can use special comments in your code to specify uncoverable criteria. Comments are of the
form:

# uncoverable <criterion> [details]

The keyword "uncoverable" must be the first text in the comment. It should be followed by the
name of the coverage criterion which is uncoverable. There may then be further information
depending on the nature of the uncoverable construct.

Statements
The "uncoverable" comment should appear on either the same line as the statement, or on the line
before it:

$impossible++; # uncoverable statement
# uncoverable statement
it_has_all_gone_horribly_wrong();

If there are multiple statements (or any other criterion) on a line you can specify which
statement is uncoverable by using the "count" attribute, count:n, which indicates that the
uncoverable statement is the nth statement on the line.

# uncoverable statement count:1
# uncoverable statement count:2
cannot_run_this(); or_this();

Branches
The "uncoverable" comment should specify whether the "true" or "false" branch is uncoverable.

# uncoverable branch true
if (pi == 3)

Both branches may be uncoverable:

# uncoverable branch true
# uncoverable branch false
if (impossible_thing_happened_one_way()) {
handle_it_one_way(); # uncoverable statement
} else {
handle_it_another_way(); # uncoverable statement
}

If there is an elsif in the branch then it can be addressed as the second branch on the line by
using the "count" attribute. Further elsifs are the third and fourth "count" value, and so on:

# uncoverable branch false count:2
if ($thing == 1) {
handle_thing_being_one();
} elsif ($thing == 2) {
handle_thing_being_tow();
} else {
die "thing can only be one or two, not $thing"; # uncoverable statement
}

Conditions
Because of the way in which Perl short-circuits boolean operations, there are three ways in
which such conditionals can be uncoverable. In the case of " $x && $y" for example, the left
operator may never be true, the right operator may never be true, and the whole operation may
never be false. These conditions may be modelled thus:

# uncoverable branch true
# uncoverable condition left
# uncoverable condition false
if ($x && !$y) {
$x++; # uncoverable statement
}

# uncoverable branch true
# uncoverable condition right
# uncoverable condition false
if (!$x && $y) {
}

"Or" conditionals are handled in a similar fashion (TODO - provide some examples) but "xor"
conditionals are not properly handled yet.

As for branches, the "count" value may be used for either conditions in elsif conditionals, or
for complex conditions.

Subroutines
A subroutine should be marked as uncoverable at the point where the first statement is marked as
uncoverable. Ideally all other criteria in the subroutine would be marked as uncoverable
automatically, but that isn't the case at the moment.

sub z {
# uncoverable subroutine
$y++; # uncoverable statement
}

Non-invasive specification
If you can't, or don't want to add coverage comments to your code, you can specify the
uncoverable information in a separate file. By default the files PWD/.uncoverable and
HOME/.uncoverable are checked. If you use the -uncoverable_file parameter then the file you
provide is checked as well as those two files.

The interface to managing this file is the cover program, and the options are:

-uncoverable_file
-add_uncoverable_point
-delete_uncoverable_point **UNIMPLEMENTED**
-clean_uncoverable_points **UNIMPLEMENTED**

The parameter for -add_uncoverable_point is a string composed of up to seven space separated
elements: "$file $criterion $line $count $type $class $note".

The contents of the uncoverable file is the same, with one point per line.

ENVIRONMENT
User variables
The -silent option is turned on when Devel::Cover is invoked via $HARNESS_PERL_SWITCHES or
$PERL5OPT. Devel::Cover tries to do the right thing when $MOD_PERL is set. $DEVEL_COVER_OPTIONS
is appended to any options passed into Devel::Cover.

Note that when Devel::Cover is invoked via an environment variable, any modules specified on the
command line, such as via the -Mmodule option, will not be covered. This is because the
environment variables are processed after the command line and any code to be covered must
appear after Devel::Cover has been loaded. To work around this, Devel::Cover can also be
specified on the command line.

Developer variables
When running Devel::Cover's own test suite, $DEVEL_COVER_DEBUG turns on debugging information,
$DEVEL_COVER_GOLDEN_VERSION overrides Devel::Cover's own idea of which golden results it should
test against, and $DEVEL_COVER_NO_COVERAGE runs the tests without collecting coverage.
$DEVEL_COVER_DB_FORMAT may be set to "Sereal", "JSON" or "Storable" to override the default
choice of DB format (Sereal, then JSON if either are available, otherwise Storable).
$DEVEL_COVER_IO_OPTIONS provides fine-grained control over the DB format. For example, setting
it to "pretty" when the format is JSON will store the DB in a readable JSON format.
$DEVEL_COVER_CPUS overrides the automated detection of the number of CPUs to use in parallel
testing.

ACKNOWLEDGEMENTS
Some code and ideas cribbed from:

* Devel::OpProf

* B::Concise

* B::Deparse