<?xml version="1.0"?>
<!-- $Id: expectation_documentation.xml 1805 2008-09-08 22:45:21Z lastcraft $ -->
<page title="Expectation documentation" here="Expectations">
    <long_title>
        Extending the SimpleTest unit tester with additional expectation classes
    </long_title>
    <content>
        <section name="mock" title="More control over mock objects">
            <p>
                The default behaviour of the
                <a local="mock_objects_documentation">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.
<php><![CDATA[
<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>
]]></php>
                Here it is sending its content to a
                <code>Writer</code> class.
                We could test this behaviour with a
                <code>MockWriter</code> like so...
<php><![CDATA[
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>
    }
}
]]></php>
                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...
<php><![CDATA[
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);
    }
}
]]></php>
                Instead of passing in the expected parameter to the
                <code>MockWriter</code> we pass an
                expectation class called
                <code>PatternExpectation</code>.
                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 <code>PatternExpectation</code> takes
                the regular expression to match in its constructor.
                Whenever a comparison is made by the <code>MockWriter</code>
                against this expectation class, it will do a
                <code>preg_match()</code> with this pattern.
                With our test case above, as long as &quot;cannot connect&quot;
                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><code>AnythingExpectation</code></td><td>Will always match</td></tr>
                    <tr><td><code>EqualExpectation</code></td><td>An equality, rather than the stronger identity comparison</td></tr>
                    <tr><td><code>NotEqualExpectation</code></td><td>An inequality comparison</td></tr>
                    <tr><td><code>IndenticalExpectation</code></td><td>The default mock object check which must match exactly</td></tr>
                    <tr><td><code>NotIndenticalExpectation</code></td><td>Inverts the mock object logic</td></tr>
                    <tr><td><code>WithinMarginExpectation</code></td><td>Compares a value to within a margin</td></tr>
                    <tr><td><code>OutsideMarginExpectation</code></td><td>Checks that a value is out side the margin</td></tr>
                    <tr><td><code>PatternExpectation</code></td><td>Uses a Perl Regex to match a string</td></tr>
                    <tr><td><code>NoPatternExpectation</code></td><td>Passes only if failing a Perl Regex</td></tr>
                    <tr><td><code>IsAExpectation</code></td><td>Checks the type or class name only</td></tr>
                    <tr><td><code>NotAExpectation</code></td><td>Opposite of the <code>IsAExpectation</code></td></tr>
                    <tr><td><code>MethodExistsExpectation</code></td><td>Checks a method is available on an object</td></tr>
                    <tr><td><code>TrueExpectation</code></td><td>Accepts any PHP variable that evaluates to true</td></tr>
                    <tr><td><code>FalseExpectation</code></td><td>Accepts any PHP variable that evaluates to false</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 <code>IsAExpectation</code> and <code>NotAExpectation</code> which takes a type
                or class name as a string.
            </p>
            <p>
                Some examples...
            </p>
            <p>
<php><![CDATA[
$mock->expectOnce('method', array(new IdenticalExpectation(14)));
]]></php>
                This is the same as <code>$mock->expectOnce('method', array(14))</code>.
<php><![CDATA[
$mock->expectOnce('method', array(new EqualExpectation(14)));
]]></php>
                This is different from the previous version in that the string
                <code>"14"</code> as a parameter will also pass.
                Sometimes the additional type checks of SimpleTest are too restrictive.
<php><![CDATA[
$mock->expectOnce('method', array(new AnythingExpectation(14)));
]]></php>
                This is the same as <code>$mock->expectOnce('method', array('*'))</code>.
<php><![CDATA[
$mock->expectOnce('method', array(new IdenticalExpectation('*')));
]]></php>
                This is handy if you want to assert a literal <code>"*"</code>.
<php><![CDATA[
new NotIdenticalExpectation(14)
]]></php>
                This matches on anything other than integer 14.
                Even the string <code>"14"</code> would pass.
<php><![CDATA[
new WithinMarginExpectation(14.0, 0.001)
]]></php>
                This will accept any value from 13.999 to 14.001 inclusive.
            </p>
        </section>
        <section name="behaviour" title="Using expectations to control stubs">
            <p>
                The expectation classes can be used not just for sending assertions
                from mock objects, but also for selecting behaviour for the
                <a local="mock_objects_documentation">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...
<php><![CDATA[
Mock::generate('Authorisation');
<strong>
$authorisation = new MockAuthorisation();
$authorisation->setReturnValue(
        'isAllowed',
        true,
        array(new IsAExpectation('Session', 'Must be a session')));
$authorisation->setReturnValue('isAllowed', false);</strong>
]]></php>
                We have set the default mock behaviour to return false when
                <code>isAllowed</code> is called.
                When we call the method with a single parameter that
                is a <code>Session</code> 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>
        </section>
        <section name="extending" title="Creating your own expectations">
            <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
                <code>SimpleExpectation</code> or forther extend a subclass...
<php><![CDATA[
<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>
]]></php>
                There are only two methods to implement.
                The <code>test()</code> method should
                evaluate to true if the expectation is to pass, and
                false otherwise.
                The <code>testMessage()</code> 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>
                Here is a more typical example, matching part of a hash...
<php><![CDATA[
<strong>class JustField extends EqualExpectation {
    private $key;
    
    function __construct($key, $expected) {
        parent::__construct($expected);
        $this->key = $key;
    }
    
    function test($compare) {
        if (! isset($compare[$this->key])) {
            return false;
        }
        return parent::test($compare[$this->key]);
    }
    
    function testMessage($compare) {
        if (! isset($compare[$this->key])) {
            return 'Key [' . $this->key . '] does not exist';
        }
        return 'Key [' . $this->key . '] -> ' .
                parent::testMessage($compare[$this->key]);
    }
}</strong>
]]></php>
                We tend to seperate message clauses with
                &quot;<![CDATA[&nbsp;->&nbsp;]]>&quot;.
                This allows derivative tools to reformat the output.
            </p>
            <p>
                Suppose some authenticator is expecting to be given
                a database row corresponding to the user, and we
                only need to confirm the username is correct.
                We can assert just their username with...
<php><![CDATA[
$mock->expectOnce('authenticate',
                  array(new JustKey('username', 'marcus')));
]]></php>
            </p>
        </section>
        <section name="unit" title="Under the bonnet of the unit tester">
            <p>
                The <a href="http://sourceforge.net/projects/simpletest/">SimpleTest unit testing framework</a>
                also uses the expectation classes internally for the
                <a local="unit_test_documentation">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 generic
                <code>SimpleTest::assert()</code> method to
                test against it directly...
<php><![CDATA[
<strong>class TestOfNetworking extends UnitTestCase {
    ...
    function testGetValidIp() {
        $server = &new Server();
        $this->assert(
                new ValidIp(),
                $server->getIp(),
                'Server IP address->%s');
    }
}</strong>
]]></php>
                <code>assert()</code> will test any expectation class directly.
            </p>
            <p>
                This is a little untidy compared with our usual
                <code>assert...()</code> syntax.
            </p>
            <p>
                For such a simple case we would normally create a
                separate assertion method on our test case rather
                than bother using the expectation class.
                If we pretend that our expectation is a little more
                complicated for a moment, so that we want to reuse it,
                we get...
<php><![CDATA[
class TestOfNetworking extends UnitTestCase {
    ...<strong>
    function assertValidIp($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>
    }
}
]]></php>
                It is rare to need the expectations for more than pattern
                matching, but these facilities do allow testers to build
                some sort of domain language for testing their application.
                Also, complex expectation classes could make the tests
                harder to read and debug.
                In effect extending the test framework to create their own tool set.
            </p>
        </section>
    </content>
    <internal>
        <link>
            Using expectations for
            <a href="#mock">more precise testing with mock objects</a>
        </link>
        <link>
            <a href="#behaviour">Changing mock object behaviour</a> with expectations
        </link>
        <link>
            <a href="#extending">Extending the expectations</a>
        </link>
        <link>
            Underneath SimpleTest <a href="#unit">uses expectation classes</a>
        </link>
    </internal>
    <external>
        <link>
            SimpleTest project page on <a href="http://sourceforge.net/projects/simpletest/">SourceForge</a>.
        </link>
        <link>
            SimpleTest download page on <a href="http://www.lastcraft.com/simple_test.php">LastCraft</a>.
        </link>
        <link>
            The expectations mimic the constraints in <a href="http://www.jmock.org/">JMock</a>.
        </link>
        <link>
            <a href="http://simpletest.org/api/">Full API for SimpleTest</a>
            from the PHPDoc.
        </link>
    </external>
    <meta>
        <keywords>
            mock objects,
            test driven development,
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            mock object constraints,
            advanced PHP unit testing,
            test first,
            test framework architecture
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        </keywords>
    </meta>
</page>
