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339 lines
14 KiB
XML
339 lines
14 KiB
XML
<?xml version="1.0"?>
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<page title="Expectation documentation" here="Expectations">
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<long_title>
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Extending the SimpleTest unit tester with additional expectation classes
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</long_title>
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<content>
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<section name="mock" title="More control over mock objects">
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<p>
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The default behaviour of the
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<a local="mock_objects_documentation">mock objects</a>
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in
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<a href="http://sourceforge.net/projects/simpletest/">SimpleTest</a>
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is either an identical match on the argument or to allow any argument at all.
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For almost all tests this is sufficient.
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Sometimes, though, you want to weaken a test case.
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</p>
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<p>
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One place where a test can be too tightly coupled is with
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text matching.
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Suppose we have a component that outputs a helpful error
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message when something goes wrong.
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You want to test that the correct error was sent, but the actual
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text may be rather long.
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If you test for the text exactly, then every time the exact wording
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of the message changes, you will have to go back and edit the test suite.
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</p>
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<p>
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For example, suppose we have a news service that has failed
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to connect to its remote source.
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<php><![CDATA[
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<strong>class NewsService {
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...
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function publish(&$writer) {
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if (! $this->isConnected()) {
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$writer->write('Cannot connect to news service "' .
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$this->_name . '" at this time. ' .
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'Please try again later.');
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}
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...
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}
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}</strong>
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]]></php>
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Here it is sending its content to a
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<code>Writer</code> class.
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We could test this behaviour with a
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<code>MockWriter</code> like so...
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<php><![CDATA[
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class TestOfNewsService extends UnitTestCase {
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...
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function testConnectionFailure() {<strong>
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$writer = &new MockWriter();
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$writer->expectOnce('write', array(
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'Cannot connect to news service ' .
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'"BBC News" at this time. ' .
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'Please try again later.'));
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$service = &new NewsService('BBC News');
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$service->publish($writer);</strong>
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}
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}
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]]></php>
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This is a good example of a brittle test.
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If we decide to add additional instructions, such as
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suggesting an alternative news source, we will break
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our tests even though no underlying functionality
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has been altered.
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</p>
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<p>
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To get around this, we would like to do a regular expression
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test rather than an exact match.
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We can actually do this with...
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<php><![CDATA[
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class TestOfNewsService extends UnitTestCase {
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...
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function testConnectionFailure() {
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$writer = &new MockWriter();<strong>
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$writer->expectOnce(
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'write',
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array(new PatternExpectation('/cannot connect/i')));</strong>
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$service = &new NewsService('BBC News');
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$service->publish($writer);
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}
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}
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]]></php>
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Instead of passing in the expected parameter to the
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<code>MockWriter</code> we pass an
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expectation class called
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<code>WantedPatternExpectation</code>.
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The mock object is smart enough to recognise this as special
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and to treat it differently.
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Rather than simply comparing the incoming argument to this
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object, it uses the expectation object itself to
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perform the test.
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</p>
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<p>
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The <code>WantedPatternExpectation</code> takes
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the regular expression to match in its constructor.
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Whenever a comparison is made by the <code>MockWriter</code>
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against this expectation class, it will do a
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<code>preg_match()</code> with this pattern.
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With our test case above, as long as "cannot connect"
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appears in the text of the string, the mock will issue a pass
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to the unit tester.
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The rest of the text does not matter.
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</p>
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<p>
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The possible expectation classes are...
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<table><tbody>
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<tr><td><code>AnythingExpectation</code></td><td>Will always match</td></tr>
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<tr><td><code>EqualExpectation</code></td><td>An equality, rather than the stronger identity comparison</td></tr>
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<tr><td><code>NotEqualExpectation</code></td><td>An inequality comparison</td></tr>
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<tr><td><code>IndenticalExpectation</code></td><td>The default mock object check which must match exactly</td></tr>
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<tr><td><code>NotIndenticalExpectation</code></td><td>Inverts the mock object logic</td></tr>
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<tr><td><code>WithinMarginExpectation</code></td><td>Compares a value to within a margin</td></tr>
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<tr><td><code>OutsideMarginExpectation</code></td><td>Checks that a value is out side the margin</td></tr>
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<tr><td><code>PatternExpectation</code></td><td>Uses a Perl Regex to match a string</td></tr>
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<tr><td><code>NoPatternExpectation</code></td><td>Passes only if failing a Perl Regex</td></tr>
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<tr><td><code>IsAExpectation</code></td><td>Checks the type or class name only</td></tr>
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<tr><td><code>NotAExpectation</code></td><td>Opposite of the <code>IsAExpectation</code></td></tr>
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<tr><td><code>MethodExistsExpectation</code></td><td>Checks a method is available on an object</td></tr>
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</tbody></table>
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Most take the expected value in the constructor.
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The exceptions are the pattern matchers, which take a regular expression,
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and the <code>IsAExpectation</code> and <code>NotAExpectation</code> which takes a type
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or class name as a string.
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</p>
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<p>
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Some examples...
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</p>
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<p>
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<php><![CDATA[
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$mock->expectOnce('method', array(new IdenticalExpectation(14)));
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]]></php>
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This is the same as <code>$mock->expectOnce('method', array(14))</code>.
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<php><![CDATA[
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$mock->expectOnce('method', array(new EqualExpectation(14)));
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]]></php>
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This is different from the previous version in that the string
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<code>"14"</code> as a parameter will also pass.
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Sometimes the additional type checks of SimpleTest are too restrictive.
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<php><![CDATA[
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$mock->expectOnce('method', array(new AnythingExpectation(14)));
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]]></php>
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This is the same as <code>$mock->expectOnce('method', array('*'))</code>.
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<php><![CDATA[
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$mock->expectOnce('method', array(new IdenticalExpectation('*')));
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]]></php>
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This is handy if you want to assert a literal <code>"*"</code>.
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<php><![CDATA[
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new NotIdenticalExpectation(14)
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]]></php>
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This matches on anything other than integer 14.
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Even the string <code>"14"</code> would pass.
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<php><![CDATA[
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new WithinMarginExpectation(14.0, 0.001)
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]]></php>
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This will accept any value from 13.999 to 14.001 inclusive.
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</p>
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</section>
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<section name="behaviour" title="Using expectations to control stubs">
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<p>
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The expectation classes can be used not just for sending assertions
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from mock objects, but also for selecting behaviour for the
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<a local="mock_objects_documentation">mock objects</a>.
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Anywhere a list of arguments is given, a list of expectation objects
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can be inserted instead.
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</p>
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<p>
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Suppose we want a mock authorisation server to simulate a successful login,
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but only if it receives a valid session object.
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We can do this as follows...
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<php><![CDATA[
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Mock::generate('Authorisation');
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<strong>
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$authorisation = new MockAuthorisation();
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$authorisation->setReturnValue(
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'isAllowed',
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true,
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array(new IsAExpectation('Session', 'Must be a session')));
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$authorisation->setReturnValue('isAllowed', false);</strong>
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]]></php>
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We have set the default mock behaviour to return false when
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<code>isAllowed</code> is called.
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When we call the method with a single parameter that
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is a <code>Session</code> object, it will return true.
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We have also added a second parameter as a message.
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This will be displayed as part of the mock object
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failure message if this expectation is the cause of
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a failure.
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</p>
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<p>
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This kind of sophistication is rarely useful, but is included for
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completeness.
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</p>
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</section>
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<section name="extending" title="Creating your own expectations">
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<p>
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The expectation classes have a very simple structure.
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So simple that it is easy to create your own versions for
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commonly used test logic.
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</p>
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<p>
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As an example here is the creation of a class to test for
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valid IP addresses.
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In order to work correctly with the stubs and mocks the new
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expectation class should extend
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<code>SimpleExpectation</code>...
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<php><![CDATA[
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<strong>class ValidIp extends SimpleExpectation {
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function test($ip) {
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return (ip2long($ip) != -1);
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}
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function testMessage($ip) {
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return "Address [$ip] should be a valid IP address";
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}
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}</strong>
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]]></php>
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There are only two methods to implement.
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The <code>test()</code> method should
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evaluate to true if the expectation is to pass, and
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false otherwise.
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The <code>testMessage()</code> method
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should simply return some helpful text explaining the test
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that was carried out.
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</p>
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<p>
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This class can now be used in place of the earlier expectation
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classes.
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</p>
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</section>
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<section name="unit" title="Under the bonnet of the unit tester">
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<p>
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The <a href="http://sourceforge.net/projects/simpletest/">SimpleTest unit testing framework</a>
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also uses the expectation classes internally for the
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<a local="unit_test_documentation">UnitTestCase class</a>.
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We can also take advantage of these mechanisms to reuse our
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homebrew expectation classes within the test suites directly.
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</p>
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<p>
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The most crude way of doing this is to use the
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<code>SimpleTest::assert()</code> method to
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test against it directly...
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<php><![CDATA[
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<strong>class TestOfNetworking extends UnitTestCase {
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...
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function testGetValidIp() {
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$server = &new Server();
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$this->assert(
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new ValidIp(),
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$server->getIp(),
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'Server IP address->%s');
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}
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}</strong>
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]]></php>
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This is a little untidy compared with our usual
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<code>assert...()</code> syntax.
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</p>
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<p>
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For such a simple case we would normally create a
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separate assertion method on our test case rather
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than bother using the expectation class.
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If we pretend that our expectation is a little more
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complicated for a moment, so that we want to reuse it,
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we get...
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<php><![CDATA[
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class TestOfNetworking extends UnitTestCase {
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...<strong>
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function assertValidIp($ip, $message = '%s') {
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$this->assert(new ValidIp(), $ip, $message);
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}</strong>
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function testGetValidIp() {
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$server = &new Server();<strong>
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$this->assertValidIp(
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$server->getIp(),
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'Server IP address->%s');</strong>
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}
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}
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]]></php>
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It is unlikely we would ever need this degree of control
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over the testing machinery.
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It is rare to need the expectations for more than pattern
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matching.
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Also, complex expectation classes could make the tests
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harder to read and debug.
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These mechanisms are really of most use to authors of systems
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that will extend the test framework to create their own tool set.
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</p>
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</section>
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</content>
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<internal>
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<link>
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Using expectations for
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<a href="#mock">more precise testing with mock objects</a>
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</link>
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<link>
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<a href="#behaviour">Changing mock object behaviour</a> with expectations
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</link>
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<link>
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<a href="#extending">Extending the expectations</a>
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</link>
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<link>
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Underneath SimpleTest <a href="#unit">uses expectation classes</a>
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</link>
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</internal>
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<external>
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<link>
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SimpleTest project page on <a href="http://sourceforge.net/projects/simpletest/">SourceForge</a>.
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</link>
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<link>
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SimpleTest download page on <a href="http://www.lastcraft.com/simple_test.php">LastCraft</a>.
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</link>
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<link>
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The expectations mimic the constraints in <a href="http://www.jmock.org/">JMock</a>.
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</link>
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<link>
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<a href="http://simpletest.sourceforge.net/">Full API for SimpleTest</a>
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from the PHPDoc.
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</link>
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</external>
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<meta>
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<keywords>
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mock objects,
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test driven development,
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inheritance of expectations,
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mock object constraints,
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advanced PHP unit testing,
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test first,
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test framework architecture
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expectations in simpletest
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test cases
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server stubs
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</keywords>
|
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</meta>
|
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</page>
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