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Extending the SimpleTest unit tester with additional expectation classes
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<h1>Expectation documentation</h1>
This page...
<ul>
<li>
Using expectations for
<a href="#mock">more precise testing with mock objects</a>
</li>
<li>
<a href="#behaviour">Changing mock object behaviour</a> with expectations
</li>
<li>
<a href="#extending">Extending the expectations</a>
</li>
<li>
Underneath SimpleTest <a href="#unit">uses expectation classes</a>
</li>
</ul>
<div class="content">
<p><a class="target" name="mock"><h2>More control over mock objects</h2></a></p>
<p>
The default behaviour of the
<a href="mock_objects_documentation.html">mock objects</a>
in
<a href="http://sourceforge.net/projects/simpletest/">SimpleTest</a>
is either an identical match on the argument or to allow any argument at all.
For almost all tests this is sufficient.
Sometimes, though, you want to weaken a test case.
</p>
<p>
One place where a test can be too tightly coupled is with
text matching.
Suppose we have a component that outputs a helpful error
message when something goes wrong.
You want to test that the correct error was sent, but the actual
text may be rather long.
If you test for the text exactly, then every time the exact wording
of the message changes, you will have to go back and edit the test suite.
</p>
<p>
For example, suppose we have a news service that has failed
to connect to its remote source.
<pre>
<strong>class NewsService {
...
function publish(&$writer) {
if (! $this->isConnected()) {
$writer->write('Cannot connect to news service "' .
$this->_name . '" at this time. ' .
'Please try again later.');
}
...
}
}</strong>
</pre>
Here it is sending its content to a
<span class="new_code">Writer</span> class.
We could test this behaviour with a
<span class="new_code">MockWriter</span> like so...
<pre>
class TestOfNewsService extends UnitTestCase {
...
function testConnectionFailure() {<strong>
$writer = &new MockWriter();
$writer->expectOnce('write', array(
'Cannot connect to news service ' .
'"BBC News" at this time. ' .
'Please try again later.'));
$service = &new NewsService('BBC News');
$service->publish($writer);</strong>
}
}
</pre>
This is a good example of a brittle test.
If we decide to add additional instructions, such as
suggesting an alternative news source, we will break
our tests even though no underlying functionality
has been altered.
</p>
<p>
To get around this, we would like to do a regular expression
test rather than an exact match.
We can actually do this with...
<pre>
class TestOfNewsService extends UnitTestCase {
...
function testConnectionFailure() {
$writer = &new MockWriter();<strong>
$writer->expectOnce(
'write',
array(new PatternExpectation('/cannot connect/i')));</strong>
$service = &new NewsService('BBC News');
$service->publish($writer);
}
}
</pre>
Instead of passing in the expected parameter to the
<span class="new_code">MockWriter</span> we pass an
expectation class called
<span class="new_code">WantedPatternExpectation</span>.
The mock object is smart enough to recognise this as special
and to treat it differently.
Rather than simply comparing the incoming argument to this
object, it uses the expectation object itself to
perform the test.
</p>
<p>
The <span class="new_code">WantedPatternExpectation</span> takes
the regular expression to match in its constructor.
Whenever a comparison is made by the <span class="new_code">MockWriter</span>
against this expectation class, it will do a
<span class="new_code">preg_match()</span> with this pattern.
With our test case above, as long as "cannot connect"
appears in the text of the string, the mock will issue a pass
to the unit tester.
The rest of the text does not matter.
</p>
<p>
The possible expectation classes are...
<table><tbody>
<tr>
<td><span class="new_code">AnythingExpectation</span></td>
<td>Will always match</td>
</tr>
<tr>
<td><span class="new_code">EqualExpectation</span></td>
<td>An equality, rather than the stronger identity comparison</td>
</tr>
<tr>
<td><span class="new_code">NotEqualExpectation</span></td>
<td>An inequality comparison</td>
</tr>
<tr>
<td><span class="new_code">IndenticalExpectation</span></td>
<td>The default mock object check which must match exactly</td>
</tr>
<tr>
<td><span class="new_code">NotIndenticalExpectation</span></td>
<td>Inverts the mock object logic</td>
</tr>
<tr>
<td><span class="new_code">WithinMarginExpectation</span></td>
<td>Compares a value to within a margin</td>
</tr>
<tr>
<td><span class="new_code">OutsideMarginExpectation</span></td>
<td>Checks that a value is out side the margin</td>
</tr>
<tr>
<td><span class="new_code">PatternExpectation</span></td>
<td>Uses a Perl Regex to match a string</td>
</tr>
<tr>
<td><span class="new_code">NoPatternExpectation</span></td>
<td>Passes only if failing a Perl Regex</td>
</tr>
<tr>
<td><span class="new_code">IsAExpectation</span></td>
<td>Checks the type or class name only</td>
</tr>
<tr>
<td><span class="new_code">NotAExpectation</span></td>
<td>Opposite of the <span class="new_code">IsAExpectation</span>
</td>
</tr>
<tr>
<td><span class="new_code">MethodExistsExpectation</span></td>
<td>Checks a method is available on an object</td>
</tr>
</tbody></table>
Most take the expected value in the constructor.
The exceptions are the pattern matchers, which take a regular expression,
and the <span class="new_code">IsAExpectation</span> and <span class="new_code">NotAExpectation</span> which takes a type
or class name as a string.
</p>
<p>
Some examples...
</p>
<p>
<pre>
$mock->expectOnce('method', array(new IdenticalExpectation(14)));
</pre>
This is the same as <span class="new_code">$mock->expectOnce('method', array(14))</span>.
<pre>
$mock->expectOnce('method', array(new EqualExpectation(14)));
</pre>
This is different from the previous version in that the string
<span class="new_code">"14"</span> as a parameter will also pass.
Sometimes the additional type checks of SimpleTest are too restrictive.
<pre>
$mock->expectOnce('method', array(new AnythingExpectation(14)));
</pre>
This is the same as <span class="new_code">$mock->expectOnce('method', array('*'))</span>.
<pre>
$mock->expectOnce('method', array(new IdenticalExpectation('*')));
</pre>
This is handy if you want to assert a literal <span class="new_code">"*"</span>.
<pre>
new NotIdenticalExpectation(14)
</pre>
This matches on anything other than integer 14.
Even the string <span class="new_code">"14"</span> would pass.
<pre>
new WithinMarginExpectation(14.0, 0.001)
</pre>
This will accept any value from 13.999 to 14.001 inclusive.
</p>
<p><a class="target" name="behaviour"><h2>Using expectations to control stubs</h2></a></p>
<p>
The expectation classes can be used not just for sending assertions
from mock objects, but also for selecting behaviour for the
<a href="mock_objects_documentation.html">mock objects</a>.
Anywhere a list of arguments is given, a list of expectation objects
can be inserted instead.
</p>
<p>
Suppose we want a mock authorisation server to simulate a successful login,
but only if it receives a valid session object.
We can do this as follows...
<pre>
Mock::generate('Authorisation');
<strong>
$authorisation = new MockAuthorisation();
$authorisation->setReturnValue(
'isAllowed',
true,
array(new IsAExpectation('Session', 'Must be a session')));
$authorisation->setReturnValue('isAllowed', false);</strong>
</pre>
We have set the default mock behaviour to return false when
<span class="new_code">isAllowed</span> is called.
When we call the method with a single parameter that
is a <span class="new_code">Session</span> object, it will return true.
We have also added a second parameter as a message.
This will be displayed as part of the mock object
failure message if this expectation is the cause of
a failure.
</p>
<p>
This kind of sophistication is rarely useful, but is included for
completeness.
</p>
<p><a class="target" name="extending"><h2>Creating your own expectations</h2></a></p>
<p>
The expectation classes have a very simple structure.
So simple that it is easy to create your own versions for
commonly used test logic.
</p>
<p>
As an example here is the creation of a class to test for
valid IP addresses.
In order to work correctly with the stubs and mocks the new
expectation class should extend
<span class="new_code">SimpleExpectation</span>...
<pre>
<strong>class ValidIp extends SimpleExpectation {
function test($ip) {
return (ip2long($ip) != -1);
}
function testMessage($ip) {
return "Address [$ip] should be a valid IP address";
}
}</strong>
</pre>
There are only two methods to implement.
The <span class="new_code">test()</span> method should
evaluate to true if the expectation is to pass, and
false otherwise.
The <span class="new_code">testMessage()</span> method
should simply return some helpful text explaining the test
that was carried out.
</p>
<p>
This class can now be used in place of the earlier expectation
classes.
</p>
<p><a class="target" name="unit"><h2>Under the bonnet of the unit tester</h2></a></p>
<p>
The <a href="http://sourceforge.net/projects/simpletest/">SimpleTest unit testing framework</a>
also uses the expectation classes internally for the
<a href="unit_test_documentation.html">UnitTestCase class</a>.
We can also take advantage of these mechanisms to reuse our
homebrew expectation classes within the test suites directly.
</p>
<p>
The most crude way of doing this is to use the
<span class="new_code">SimpleTest::assert()</span> method to
test against it directly...
<pre>
<strong>class TestOfNetworking extends UnitTestCase {
...
function testGetValidIp() {
$server = &new Server();
$this->assert(
new ValidIp(),
$server->getIp(),
'Server IP address->%s');
}
}</strong>
</pre>
This is a little untidy compared with our usual
<span class="new_code">assert...()</span> syntax.
</p>
<p>
For such a simple case we would normally create a
separate assertion method on our test case rather
than bother using the expectation class.
If we pretend that our expectation is a little more
complicated for a moment, so that we want to reuse it,
we get...
<pre>
class TestOfNetworking extends UnitTestCase {
...<strong>
function assertValidIp($ip, $message = '%s') {
$this->assert(new ValidIp(), $ip, $message);
}</strong>
function testGetValidIp() {
$server = &new Server();<strong>
$this->assertValidIp(
$server->getIp(),
'Server IP address->%s');</strong>
}
}
</pre>
It is unlikely we would ever need this degree of control
over the testing machinery.
It is rare to need the expectations for more than pattern
matching.
Also, complex expectation classes could make the tests
harder to read and debug.
These mechanisms are really of most use to authors of systems
that will extend the test framework to create their own tool set.
</p>
</div>
References and related information...
<ul>
<li>
SimpleTest project page on <a href="http://sourceforge.net/projects/simpletest/">SourceForge</a>.
</li>
<li>
SimpleTest download page on <a href="http://www.lastcraft.com/simple_test.php">LastCraft</a>.
</li>
<li>
The expectations mimic the constraints in <a href="http://www.jmock.org/">JMock</a>.
</li>
<li>
<a href="http://simpletest.org/api/">Full API for SimpleTest</a>
from the PHPDoc.
</li>
</ul>
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Copyright<br>Marcus Baker 2006
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