389 lines
14 KiB
HTML
389 lines
14 KiB
HTML
<html>
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<title>SimpleTest for PHP server stubs documentation</title>
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<h2>
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<a href="index.html">SimpleTest</a>
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</h2>
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<ul>
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<a href="overview.html">Overview</a>
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<a href="group_test_documentation.html">Group tests</a>
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<span class="chosen">Server stubs</span>
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<a href="mock_objects_documentation.html">Mock objects</a>
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<a href="authentication_documentation.html">Authentication</a>
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<a href="browser_documentation.html">Scriptable browser</a>
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<h1>Server stubs documentation</h1>
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<div class="content">
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<p>
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<a class="target" name="what">
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<h2>What are server stubs?</h2>
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</a>
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</p>
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<p>
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This was originally a pattern named by Robert Binder (Testing
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object-oriented systems: models, patterns, and tools,
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Addison-Wesley) in 1999.
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A server stub is a simulation of an object or component.
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It should exactly replace a component in a system for test
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or prototyping purposes, but remain lightweight.
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This allows tests to run more quickly, or if the simulated
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class has not been written, to run at all.
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</p>
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<p>
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<a class="target" name="creation">
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<h2>Creating server stubs</h2>
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</a>
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</p>
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<p>
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All we need is an existing class, say a database connection
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that looks like this...
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<pre>
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<strong>class DatabaseConnection {
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function DatabaseConnection() {
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}
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function query() {
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}
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function selectQuery() {
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}
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}</strong>
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</pre>
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The class does not need to have been implemented yet.
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To create a stub version of the class we need to include the
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server stub library and run the generator...
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<pre>
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<strong>require_once('simpletest/mock_objects.php');
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require_once('database_connection.php');
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Stub::generate('DatabaseConnection');</strong>
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</pre>
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This generates a clone class called
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<span class="new_code">StubDatabaseConnection</span>.
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We can now create instances of the new class within
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our prototype script...
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<pre>
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require_once('simpletest/mock_objects.php');
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require_once('database_connection.php');
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Stub::generate('DatabaseConnection');
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<strong>
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$connection = new StubDatabaseConnection();
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</strong>
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</pre>
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The stub version of a class has all the methods of the original
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so that operations like
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<span class="new_code">$connection->query()</span> are still
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legal.
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The return value will be <span class="new_code">null</span>,
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but we can change that with...
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<pre>
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<strong>$connection->setReturnValue('query', 37)</strong>
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</pre>
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Now every time we call
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<span class="new_code">$connection->query()</span> we get
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the result of 37.
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We can set the return value to anything, say a hash of
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imaginary database results or a list of persistent objects.
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Parameters are irrelevant here, we always get the same
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values back each time once they have been set up this way.
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That may not sound like a convincing replica of a
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database connection, but for the half a dozen lines of
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a test method it is usually all you need.
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</p>
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<p>
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<a class="target" name="patterns">
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<h2>Simulation patterns</h2>
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</a>
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</p>
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<p>
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Things aren't always that simple though.
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One common problem is iterators, where constantly returning
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the same value could cause an endless loop in the object
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being tested.
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For these we need to set up sequences of values.
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Let's say we have a simple iterator that looks like this...
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<pre>
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class Iterator {
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function Iterator() {
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}
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function next() {
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}
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}
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</pre>
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This is about the simplest iterator you could have.
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Assuming that this iterator only returns text until it
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reaches the end, when it returns false, we can simulate it
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with...
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<pre>
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<strong>Stub::generate('Iterator');
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$iterator = new StubIterator();
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$iterator->setReturnValue('next', false);
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$iterator->setReturnValueAt(0, 'next', 'First string');
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$iterator->setReturnValueAt(1, 'next', 'Second string');</strong>
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</pre>
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When <span class="new_code">next()</span> is called on the
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stub iterator it will first return "First string",
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on the second call "Second string" will be returned
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and on any other call <span class="new_code">false</span> will
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be returned.
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The sequenced return values take precedence over the constant
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return value.
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The constant one is a kind of default if you like.
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</p>
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<p>
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Another tricky situation is an overloaded
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<span class="new_code">get()</span> operation.
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An example of this is an information holder with name/value pairs.
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Say we have a configuration class like...
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<pre>
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class Configuration {
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function Configuration() {
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}
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function getValue($key) {
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}
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}
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</pre>
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This is a classic situation for using stub objects as
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actual configuration will vary from machine to machine,
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hardly helping the reliability of our tests if we use it
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directly.
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The problem though is that all the data comes through the
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<span class="new_code">getValue()</span> method and yet
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we want different results for different keys.
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Luckily the stubs have a filter system...
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<pre>
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<strong>Stub::generate('Configuration');
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$config = &new StubConfiguration();
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$config->setReturnValue('getValue', 'primary', array('db_host'));
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$config->setReturnValue('getValue', 'admin', array('db_user'));
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$config->setReturnValue('getValue', 'secret', array('db_password'));</strong>
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</pre>
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The extra parameter is a list of arguments to attempt
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to match.
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In this case we are trying to match only one argument which
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is the look up key.
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Now when the server stub has the
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<span class="new_code">getValue()</span> method invoked
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like this...
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<pre>
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$config->getValue('db_user');
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</pre>
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...it will return "admin".
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It finds this by attempting to match the calling arguments
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to its list of returns one after another until
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a complete match is found.
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</p>
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<p>
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You can set a default argument argument like so...
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<pre>
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<strong>
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$config->setReturnValue('getValue', false, array('*'));</strong>
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</pre>
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This is not the same as setting the return value without
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any argument requirements like this...
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<pre>
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<strong>
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$config->setReturnValue('getValue', false);</strong>
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</pre>
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In the first case it will accept any single argument,
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but exactly one is required.
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In the second case any number of arguments will do and
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it acts as a catchall after all other matches.
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Note that if we add further single parameter options after
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the wildcard in the first case, they will be ignored as the wildcard
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will match first.
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With complex parameter lists the ordering could be important
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or else desired matches could be masked by earlier wildcard
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ones.
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Declare the most specific matches first if you are not sure.
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</p>
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<p>
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There are times when you want a specific object to be
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dished out by the stub rather than just a copy.
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The PHP copy semantics force us to use a different method
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for this.
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You might be simulating a container for example...
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<pre>
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class Thing {
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}
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class Vector {
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function Vector() {
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}
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function get($index) {
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}
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}
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</pre>
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In this case you can set a reference into the stub's
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return list...
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<pre>
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Stub::generate('Vector');
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$thing = new Thing();<strong>
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$vector = &new StubVector();
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$vector->setReturnReference('get', $thing, array(12));</strong>
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</pre>
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With this arrangement you know that every time
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<span class="new_code">$vector->get(12)</span> is
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called it will return the same
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<span class="new_code">$thing</span> each time.
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</p>
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<p>
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These three factors, timing, parameters and whether to copy,
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can be combined orthogonally.
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For example...
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<pre>
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$complex = &new StubComplexThing();
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$stuff = new Stuff();<strong>
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$complex->setReturnReferenceAt(3, 'get', $stuff, array('*', 1));</strong>
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</pre>
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This will return the <span class="new_code">$stuff</span> only on the third
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call and only if two parameters were set the second of
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which must be the integer 1.
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That should cover most simple prototyping situations.
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</p>
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<p>
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A final tricky case is one object creating another, known
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as a factory pattern.
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Suppose that on a successful query to our imaginary
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database, a result set is returned as an iterator with
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each call to <span class="new_code">next()</span> giving
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one row until false.
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This sounds like a simulation nightmare, but in fact it can all
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be stubbed using the mechanics above.
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</p>
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<p>
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Here's how...
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<pre>
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Stub::generate('DatabaseConnection');
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Stub::generate('ResultIterator');
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class DatabaseTest extends UnitTestCase {
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function testUserFinder() {<strong>
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$result = &new StubResultIterator();
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$result->setReturnValue('next', false);
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$result->setReturnValueAt(0, 'next', array(1, 'tom'));
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$result->setReturnValueAt(1, 'next', array(3, 'dick'));
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$result->setReturnValueAt(2, 'next', array(6, 'harry'));
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$connection = &new StubDatabaseConnection();
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$connection->setReturnValue('query', false);
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$connection->setReturnReference(
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'query',
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$result,
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array('select id, name from users'));</strong>
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$finder = &new UserFinder($connection);
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$this->assertIdentical(
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$finder->findNames(),
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array('tom', 'dick', 'harry'));
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}
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}
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</pre>
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Now only if our
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<span class="new_code">$connection</span> is called with the correct
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<span class="new_code">query()</span> will the
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<span class="new_code">$result</span> be returned that is
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itself exhausted after the third call to <span class="new_code">next()</span>.
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This should be enough
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information for our <span class="new_code">UserFinder</span> class,
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the class actually
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being tested here, to come up with goods.
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A very precise test and not a real database in sight.
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</p>
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<p>
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<a class="target" name="options">
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<h2>Stub creation options</h2>
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</a>
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</p>
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<p>
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There are some additional options when creating stubs.
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At the generation stage we can change the class name...
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<pre>
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<strong>Stub::generate('Iterator', 'MyStubIterator');
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$iterator = &new MyStubIterator();
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</strong>
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</pre>
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This is not very useful in itself as there would be no difference
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in this class and the default except for the name.
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However we can also add additional methods not found in the
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original interface...
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<pre>
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class Iterator {
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}
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<strong>Stub::generate('Iterator', 'PrototypeIterator', array('next', 'isError'));
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$iterator = &new PrototypeIterator();
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$iterator->setReturnValue('next', 0);
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</strong>
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</pre>
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The <span class="new_code">next()</span> and
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<span class="new_code">isError()</span> methods can now have
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return values set just as if they existed in the original class.
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</p>
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<p>
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One other esoteric way of customising the stubs is to change
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the default wildcard used for parameter matching.
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<pre>
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<strong>Stub::generate('Connection');
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$iterator = &new StubConnection('wild');
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$iterator->setReturnValue('query', array('id' => 33), array('wild'));
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</strong>
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</pre>
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The only reason to do this is if you genuinely wanted to test
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against the literal string "*" and didn't want it
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interpreted as "any".
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</p>
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</div>
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<div class="copyright">
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Copyright<br>Marcus Baker, Jason Sweat, Perrick Penet 2004
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</div>
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</body>
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</html>
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