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<title>Custom predicate support</title>
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</a><b>Custom predicate support</b>
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<div class="titlepage"><div><div><h4 class="title">
<a name="utf.testing-tools.custom-predicate"></a>Custom predicate support</h4></div></div></div>
<p class="first-line-indented">
Even though supplied testing tools cover wide range of possible checks and provide detailed report on cause of error
in some cases you may want to implement and use custom predicate that perform complex check and produce intelligent
report on failure. To satisfy this need testing tools implement custom predicate support. There two layers of custom
predicate support implemented by testing tools toolbox: with and without custom error message generation.
</p>
<p class="first-line-indented">
The first layer is supported by BOOST_CHECK_PREDICATE family of testing tools. You can use it to check any custom
predicate that reports the result as boolean value. The values of the predicate arguments are reported by the tool
automatically in case of failure.
</p>
<div class="example">
<a name="utf.testing-tools.custom-predicate.example30"></a><p class="title"><b>Example36.Custom predicate support using BOOST_CHECK_PREDICATE</b></p>
<div class="example-contents">
<pre class="programlisting">#define BOOST_TEST_MODULE example
#include <boost/test/included/unit_test.hpp>
//____________________________________________________________________________//
bool is_even( int i ) { return i%2 == 0; }
BOOST_AUTO_TEST_CASE( test_is_even )
{
BOOST_CHECK_PREDICATE( is_even, (14) );
int i = 17;
BOOST_CHECK_PREDICATE( is_even, (i) );
}
//____________________________________________________________________________//
</pre>
<table class="simplelist" border="0" summary="Simple list"><tr>
<td><code class="literal"><a href="../../../src/examples/example30.cpp" target="_top">Source code</a></code></td>
<td> | </td>
<td><code class="literal"><a href="#" target="_top" id="id658382" onclick="toggle_element( 'example30-output', 'id658382', 'Show output', 'Hide output' ); return false;">Show output</a></code></td>
</tr></table>
<pre class="example-output" id="example30-output">> example
Running 1 test case...
test.cpp(13): error in "test_is_even": check is_even( i ) failed for ( 17 )
*** 1 failure detected in test suite "example"
</pre>
</div>
</div>
<br class="example-break"><p class="first-line-indented">
To use second layer your predicate have to return
<code class="computeroutput">boost::test_tools::predicate_result</code>. This class encapsulates boolean result value along
with any error or information message you opt to report.
</p>
<p class="first-line-indented">
Usually you construct the instance of class <code class="computeroutput">boost::test_tools::predicate_result</code> inside your
predicate function and return it by value. The constructor expects one argument - the boolean result value. The
constructor is implicit, so you can simply return boolean value from your predicate and
<code class="computeroutput">boost::test_tools::predicate_result</code> is constructed automatically to hold your value and empty
message. You can also assign boolean value to the constructed instance. You can check the current predicate value by
using <code class="computeroutput">operator!</code>() or directly accessing public read-only property p_predicate_value. The
error message is stored in public read-write property p_message.
</p>
<div class="example">
<a name="utf.testing-tools.custom-predicate.example31"></a><p class="title"><b>Example37.Custom predicate support using class predicate_result</b></p>
<div class="example-contents">
<pre class="programlisting">#define BOOST_TEST_MODULE example
#include <boost/test/included/unit_test.hpp>
//____________________________________________________________________________//
boost::test_tools::predicate_result
compare_lists( std::list<int> const& l1, std::list<int> const& l2 )
{
if( l1.size() != l2.size() ) {
boost::test_tools::predicate_result res( false );
res.message() << "Different sizes [" << l1.size() << "!=" << l2.size() << "]";
return res;
}
return true;
}
//____________________________________________________________________________//
BOOST_AUTO_TEST_CASE( test_list_comparizon )
{
std::list<int> l1, l2;
l1.push_back( 1 );
l1.push_back( 2 );
BOOST_CHECK( compare_lists( l1, l2 ) );
}
//____________________________________________________________________________//
</pre>
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<td><code class="literal"><a href="../../../src/examples/example31.cpp" target="_top">Source code</a></code></td>
<td> | </td>
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<pre class="example-output" id="example31-output">Running 1 test case...
test.cpp(28): error in "test_list_comparizon": check compare_lists( l1, l2 ) failed. Different sizes [2!=0]
*** 1 failure detected in test suite "example"
</pre>
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