Devel::Cover::Truth_Table(3) User Contributed Perl Documentation Devel::Cover::Truth_Table(3)NAME
Devel::Cover::Truth_Table - Truth tables for coverage objects.
VERSION
version 1.03
SYNOPSIS
use Devel::Cover::Truth_Table;
# $a || $b
my $or_tt = Devel::Cover::Truth_Table->new_primitive('or_3', 0, 1, 1);
# $c && $d
my $and_tt = Devel::Cover::Truth_Table->new_primitive('and_3', 1, 0, 1);
# merge contents of $and_tt into right column of $or_tt, to create
# $a || ($c && $d)
$or_tt->right_merge($and_tt);
# get a (sorted) textual representation
my @text = $or_tt->sort->text;
print "$_
" foreach @text;
__END__
A B C |exp|hit
--------------
0 0 X | 0 |---
0 1 0 | 0 |---
0 1 1 | 1 |+++
1 X X | 1 |+++
--------------
DESCRIPTION
This module provides methods for creating and merging conditional primitives ("$a && $b", "$c || $d", etc.) into more complex composite
expressions.
METHODS
new_primitive($op, @coverage)
Create a new truth table based on one of the built-in primitives, which are the subclasses of Devel::Cover::DB::Condition. $op is one of
the following:
and_3
"and" or "&&" with three conditional paths.
or_3
"or" or "||" with three conditional paths.
or_2
"or" or "||" with two conditional paths. (i.e., when the right hand side of the expression is a constant)
xor_4
"xor" with four conditional paths.
@coverage is a list booleans identifying which of the possible paths have been covered.
sort()
Sorts a truth table (in place) and returns the sorted object.
text()
Format a truth table to an array of strings for printing.
html()
Format a truth table in HTML.
error()
percentage()
Determines the proportion of possible conditions that have coverage.
right_merge($sub_table)
Merge entries from $sub_table into right column of table.
left_merge($sub_table)
Merge entries from $sub_table into left column of table.
SEE ALSO
Devel::Cover
BUGS
None that I'm aware of...
LICENSE
Copyright 2002 Michael Carman <mjcarman@mchsi.com>
This software is free. It is licensed under the same terms as Perl itself. The latest version should be available from: http://www.pjcj.net
perl v5.16.3 2013-05-20 Devel::Cover::Truth_Table(3)
Check Out this Related Man Page
Devel::Cover::Tutorial(3) User Contributed Perl Documentation Devel::Cover::Tutorial(3)NAME
Devel::Cover::Tutorial - An introduction to code coverage
VERSION
version 1.03
TUTORIAL
Here's part of a message I sent to perl-qa about code coverage metrics.
1.0 Introduction
It is wise to remember the following quote from Dijkstra, who said:
Testing never proves the absence of faults, it only shows their presence.
In particular, code coverage is just one weapon in the software engineer's testing arsenal.
Any discussion of code coverage metrics is hampered by the fact that many authors use different terms to describe the same kind of
coverage. Here, I shall provide only a brief introduction to some of the most common metrics.
2.0 Metrics
2.1 Statement coverage
This is the most basic form of code coverage. A statement is covered if it is executed. Note that statement != line of code. Multiple
statements on a single line can confuse issues - the reporting if nothing else.
Where there are sequences of statements without branches it is not necessary to count the execution of every statement, just one will
suffice, but people often like the count of every line to be reported, especially in summary statistics. However it is not clear to me
that this is actually useful.
This type of coverage is fairly weak in that even with 100% statement coverage there may still be serious problems in a program which could
be discovered through other types of metric.
It can be quite difficult to achieve 100% statement coverage. There may be sections of code designed to deal with error conditions, or
rarely occurring events such as a signal received during a certain section of code. There may also be code that should never be executed:
if ($param > 20)
{
die "This should never happen!";
}
It can be useful to mark such code in some way and flag an error if it is executed.
Statement coverage, or something very similar, can be called statement execution, line, block, basic block or segment coverage. I tend to
favour block coverage which does not attempt to extend its results to each statement.
2.2 Branch coverage
The goal of branch coverage is to ensure that whenever a program can jump, it jumps to all possible destinations. The most simple example
is a complete if statement:
if ($x)
{
print "a";
}
else
{
print "b";
}
In such a simple example statement coverage is as powerful, but branch coverage should also allow for the case where the else part is
missing:
if ($x)
{
print "a";
}
Full coverage is only achieved here if $x is true on one occasion and false on another.
100% branch coverage implies 100% statement coverage.
Branch coverage is also called decision or all edges coverage.
2.3 Path coverage
There are classes of errors that branch coverage cannot detect, such as:
$h = undef;
if ($x)
{
$h = { a => 1 };
}
if ($y)
{
print $h->{a};
}
100% branch coverage can be achieved by setting ($x, $y) to (1, 1) and then to (0, 0). But if we have (0, 1) then things go bang.
The purpose of path coverage is to ensure that all paths through the program are taken. In any reasonably sized program there will be an
enormous number of paths through the program and so in practice the paths can be limited to a single subroutine, if the subroutine is not
too big, or simply to two consecutive branches.
In the above example there are four paths which correspond to the truth table for $x and $y. To achieve 100% path coverage they must all
be taken. Note that missing elses count as paths.
In some cases it may be impossible to achieve 100% path coverage:
a if $x;
b;
c if $x;
50% path coverage is the best you can get here.
Loops also contribute to paths, and pose their own problems which I'll ignore for now.
100% path coverage implies 100% branch coverage.
Path coverage and some of its close cousins, are also known as predicate, basis path and LCSAJ (Linear Code Sequence and Jump) coverage.
2.4 Expression coverage
When a boolean expression is evaluated it can be useful to ensure that all the terms in the expression are exercised. For example:
a if $x || $y
The expression should be exercised with ($x, $y) set to (0, 0) (required for branch coverage), (0, 1) and (1, 0) (to ensure that $x and $y
are independent) and possibly with (1, 1).
Expression coverage gets complicated, and difficult to achieve, as the expression gets complicated.
Expressions which are not directly a part of a branching construct should also be covered:
$z = $x || $y;
a if $z;
Expression coverage is also known as condition, condition-decision and multiple decision coverage.
3.0 Other considerations
In order to get people to actually use code coverage it needs to be simple to use. It should also be simple to understand the results and
to rectify any problems thrown up. Finally, if the overhead is too great it won't get used either.
So there's a basic tutorial on code coverage, or at least my version of it. Typing a few of these terms into google will probably provide
a basis for future research.
LICENCE
Copyright 2001-2013, Paul Johnson (paul@pjcj.net)
This software is free. It is licensed under the same terms as Perl itself.
The latest version of this software should be available from my homepage: http://www.pjcj.net
perl v5.16.3 2013-05-20 Devel::Cover::Tutorial(3)