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Assert Task</title>
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<h2 class="title">
<a name="Assert">
</a>
Assert Task</h2>
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<div>
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<p>
The Assert task adds an assertion capability to Ant projects. This task works in a manner very similar to the Java <tt class="computeroutput">
assert</tt>
keyword, and provides a limited "design by contract" facility to Ant. This is very useful for testing build scripts prior to putting them into production.
</p>
<p>
The Assert task verifies that a given property has a
given value and throws a BuildException if the property value is not as expected
or the property does not exist.
</p>
<p>
Also like Java's <tt class="computeroutput">
assert</tt>
keyword, the Assert task must be 'turned on' using the property <tt class="computeroutput">
ant.enable.asserts</tt>
. If not set, or is set to <tt class="computeroutput">
false</tt>
, the Assert task works exactly like the Sequential task. If the <a href="variable_task.html" title="Variable Task">
Variable task</a>
is used to define this property, then it can be turned on and off as needed throughout a build.
</p>
<p>
This task can hold other tasks including Assert.
</p>
<p>
The Assert task may contain one 'bool' element. The 'bool' element is identical to the ConditionTask, but unlike the ConditionTask, is actually a Task. The 'bool' element can contain all the conditions permitted by the ConditionTask, plus the <a href="bk03ch05s02.html" title="More Conditions">
IsPropertyTrue</a>
, <a href="more_conditions.html" title="More Conditions">
IsPropertyFalse</a>
,
<a href="more_conditions.html" title="More Conditions">
StartsWith</a>
,
<a href="more_conditions.html" title="More Conditions">
EndsWith</a>
,
<a href="more_conditions.html" title="More Conditions">
IsGreaterThan</a>
,
<a href="more_conditions.html" title="More Conditions">
IsLessThan</a>
and conditions.
See the If task for examples of using these conditionals.
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<p>
<div class="table">
<a name="N10583">
</a>
<p class="title">
<b>
Table 4.1. Assert Task Attributes</b>
</p>
<table summary="Assert Task Attributes" border="1">
<colgroup>
<col>
<col>
<col>
<col>
</colgroup>
<thead>
<tr>
<th>
Attribute</th>
<th>
Description</th>
<th>
Default</th>
<th>
Required</th>
</tr>
</thead>
<tbody>
<tr>
<td>
name</td>
<td>
The name of the property to test for.</td>
<td>
none</td>
<td>
Yes</td>
</tr>
<tr>
<td>
exists</td>
<td>
Test for existence or non-existence of the property.</td>
<td>
True</td>
<td>
No</td>
</tr>
<tr>
<td>
value</td>
<td>
The value to test for, implies 'exists=true'. If the value in the project is different than this value, a BuildException will be thrown and the build will stop.</td>
<td>
none</td>
<td>
No</td>
</tr>
<tr>
<td>
execute</td>
<td>
Should the tasks contained in this task be executed? It may be useful to set this to false when testing build files.</td>
<td>
True</td>
<td>
No</td>
</tr>
<tr>
<td>
failonerror</td>
<td>
Should the build halt if the assertion fails? Setting this to false is contrary to the intented use of assertions, but may be useful in certain situations. </td>
<td>
True</td>
<td>
No</td>
</tr>
</tbody>
</table>
</div>
</p>
<p>
As stated above, the Assert task may contain a nested "bool" task, otherwise,
the Assert task does not support any nested
elements apart from Ant tasks. Any valid Ant task may be embedded within the
assert task.
</p>
<p>
In the following example, the first <tt class="computeroutput">
assert</tt>
task checks that the <tt class="computeroutput">
wait</tt>
property exists and does not execute the <tt class="computeroutput">
echo</tt>
and <tt class="computeroutput">
sleep</tt>
tasks. The second <tt class="computeroutput">
assert</tt>
task checks that the <tt class="computeroutput">
wait</tt>
property exists, has a value of 2, and executes the <tt class="computeroutput">
echo</tt>
task.
</p>
<p>
<table border="0" bgcolor="#E0E0E0">
<tr>
<td>
<pre class="programlisting">
<property name="wait" value="2"/>
<assert name="wait" execute="false">
<echo>
Waiting ${wait} seconds...
Click the red button to stop waiting.
</echo>
<sleep seconds="${wait}"/>
</assert>
<assert name="wait" value="2" execute="true">
<echo>done waiting!</echo>
</assert>
</pre>
</td>
</tr>
</table>
</p>
<p>
The next example shows Assert being used in a unit test for the "limit" task:
<table border="0" bgcolor="#E0E0E0">
<tr>
<td>
<pre class="programlisting">
<property name="ant.enable.asserts" value="true"/>
<target name="test2">
<!-- should not stop 'sleep' task, should print out '_passed_' -->
<stopwatch name="timer"/>
<limit maxwait="5">
<sleep seconds="1"/>
<echo>_passed_</echo>
</limit>
<stopwatch name="timer" action="total"/>
<assert message="Too much time.">
<bool>
<islessthan arg1="${timer}" arg2="2"/>
</bool>
</assert>
</target>
</pre>
</td>
</tr>
</table>
</p>
<p>
If the <tt class="computeroutput">
ant.enable.asserts</tt>
property is set to false, then in the above example, the <tt class="computeroutput">
echo</tt>
, <tt class="computeroutput">
sleep</tt>
, and <tt class="computeroutput">
echo</tt>
tasks will all execute.
</p>
<hr>
<p align="center">Copyright © 2003 Ant-Contrib Project. All
rights Reserved.</p>
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