224 lines
8.2 KiB
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224 lines
8.2 KiB
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<h2>NUnit Addins</h2>
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<p>NUnit originally identified tests in the time-honored way used in many xUnit
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test frameworks. Test classes inherited from the framework's
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TestCase class. Individual test case methods were identified by having names
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starting with "test..."</p>
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<p>With NUnit 2.0, we introduced the use of attributes to identify both fixtures
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and test cases. Use of attributes in this way was a natural outcome of their
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presence in .NET and gave us a way of identifying tests that was completely
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independent of both inheritance and naming conventions.</p>
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<p>However, by moving away from an inheritance-based mechanism we no longer
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had an easy way for others to extend NUnit's internal behavior. NUnit Addins are
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intended to fill that gap, providing an mechanism to introduce new or changed
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behavior without modifying NUnit itself.</p>
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<h3>Extension Points, Extensions and Addins</h3>
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<p>NUnit provides a number of <b>Extension Points</b>, places where it is
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possible to extend its behavior. Because NUnit works with various hosts
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and uses separate AppDomains to run tests, <b>Extension Points</b> are
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categorized into three types: Core, Client and Gui. Each of these types is
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supported by a different <b>Extension Host</b>.
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<p>An NUnit <b>Addin</b> provides enhanced functionality through one or more
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extensions, which it installs at identified <b>Extension Points</b>. Each
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<b>Addin</b> is characterized by the types of extensions it supplies, so that
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an <b>Extension Host</b> knows whether to invoke it.</p>
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<blockquote>
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<p><b>Note:</b> In the current release, only Core extensions are actually
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supported. An Addin may characterize itself as a Client or Gui extension and
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will be listed as such in the <a href="addinsDialog.html">Addins Dialog</a>,
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but no other action is taken.</p>
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</blockquote>
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<h3>Addin Identification, Loading and Installation</h3>
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<p>NUnit examines all assemblies in the <b>bin/addins</b> directory, looking
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for public classes with the <b>NUnitAddinAttribute</b> and implementing the
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<b>IAddin</b> interface. It loads all those it finds as Addins.</p>
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<p><b>NUnitAddinAttribute</b> supports three optional named parameters: Type,
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Name and Description. Name and Description are strings representing the name
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of the extension and a description of what it does. If no name is provided,
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the name of the class is used. Type may be any one or a combination of the
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ExtensionType enum members:
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<pre>
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[Flags]
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public enum ExtensionType
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{
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Core=1,
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Client=2,
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Gui=4
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}
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</pre>
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The values may be or'ed together, allowing for future Addins that require
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extensions at multiple levels of the application. If not provided, Type
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defaults to ExtensionType.Core.</p>
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<p>The <b>IAddin</b> interface, which must be implemented by each Addin,
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is defined as follows:</p>
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<pre>
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public interface IAddin
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{
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bool Install( IExtensionHost host );
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}
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</pre>
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<p> The <b>Install</b> method is called by each host for which the addin has
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specified an ExtensionType. The addin should check that the necessary extension
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points are available and install itself, returning true for success or false
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for failure to install. The method will be called once for each extension
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host and - for Core extensions - each time a new test domain is loaded.</p>
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<p>The Install method uses the <b>IExtensionHost</b> interface to locate
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extension points. It is defined as follows:</p>
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<pre>
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public interface IExtensionHost
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{
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IExtensionPoint[] ExtensionPoints { get; }
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IExtensionPoint GetExtensionPoint( string name );
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ExtensionType ExtensionTypes { get; }
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}
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</pre>
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<p>The <b>ExtensionPoints</b> property returns an array of all extension points
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for those extensions that need the information. The <b>ExtensionTypes</b>
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property returns the flags for the type of extension supported by this host,
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allowing, for example, Gui extensions to only load in a Gui host.</p>
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<p>Most addins will only need to use the <b>GetExtensionPoint</b> method to
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get the interface to a particular extension point. The <b>IExtensionPoint</b>
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interface is defined as follows:</p>
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<pre>
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public interface IExtensionPoint
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{
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string Name { get; }
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IExtensionHost Host { get; }
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void Install( object extension );
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void Remove( object extension );
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}
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</pre>
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<p>Once again, most addins will only need to use one method - the
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<b>Install</b> method in this case. This method passes an extension object
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to the <b>Extension Point</b> where it is installed. Generally, extensions
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do not need to remove themselves once installed, but the method is
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provided in any case.</p>
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<p>With NUnit 2.5, an additional interface, <b>IExtensionPoint2</b> is
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available. It derives from <b>IExtensionPoint</b> and also allows setting
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the priority order in which the extension will be called in comparison to
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other extensions on the same extension point. The interface is defined
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as follows:
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<pre>
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public interface IExtensionPoint2 : IExtensionPoint
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{
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void Install( object extension, int priority );
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}
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</pre>
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<p>Only extension points that use a priority scheme implement this interface.
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In general, extension points with a priority scheme will use a default value
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for priority if the Install method without a priority is called.
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<p>In the NUnit 2.5 release, only the <b>TestDecorators</b> extension point implements
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<b>IExtensionPoint2</b>.
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<h3>Extension Point Details</h3>
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<p>Depending on the particular extension point, the object passed will
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need to implement one or more interfaces. The following <b>ExtensionPoints</b>
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are implemented in this release of NUnit:
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<ul>
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<li><a href="suiteBuilders.html">SuiteBuilders</a> <li><a href="testcaseBuilders.html">TestCaseBuilders</a> <li><a href="testDecorators.html">TestDecorators</a> <li><a href="testcaseProviders.html">TestCaseProviders</a> <li><a href="datapointProviders.html">DataPointProviders</a> <li><a href="eventListeners.html">EventListeners</a></ul></p>
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<p>For examples of implementing each type of extension, see the Extensibility
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samples provided with NUnit. More complete examples are available in the
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code of NUnit itself, since NUnit uses the same mechanism internally.</p>
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<h4>See also...</h4>
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<ul>
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<li><a href="extensionTips.html">Tips for Writing Extensions</a></ul>
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Copyright © 2010 Charlie Poole. All Rights Reserved.
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