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| 24 |
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| 25 | <div id="content">
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| 26 |
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| 27 | <h2>NUnit Addins</h2>
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| 28 |
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| 29 | <p>NUnit originally identified tests in the time-honored way used in many xUnit
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| 30 | test frameworks. Test classes inherited from the framework's
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| 31 | TestCase class. Individual test case methods were identified by having names
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| 32 | starting with "test..."</p>
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| 33 |
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| 34 | <p>With NUnit 2.0, we introduced the use of attributes to identify both fixtures
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| 35 | and test cases. Use of attributes in this way was a natural outcome of their
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| 36 | presence in .NET and gave us a way of identifying tests that was completely
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| 37 | independent of both inheritance and naming conventions.</p>
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| 38 |
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| 39 | <p>However, by moving away from an inheritance-based mechanism we no longer
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| 40 | had an easy way for others to extend NUnit's internal behavior. NUnit Addins are
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| 41 | intended to fill that gap, providing an mechanism to introduce new or changed
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| 42 | behavior without modifying NUnit itself.</p>
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| 43 |
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| 44 | <h3>Extension Points, Extensions and Addins</h3>
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| 45 |
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| 46 | <p>NUnit provides a number of <b>Extension Points</b>, places where it is
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| 47 | possible to extend its behavior. Because NUnit works with various hosts
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| 48 | and uses separate AppDomains to run tests, <b>Extension Points</b> are
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| 49 | categorized into three types: Core, Client and Gui. Each of these types is
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| 50 | supported by a different <b>Extension Host</b>.
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| 51 |
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| 52 | <p>An NUnit <b>Addin</b> provides enhanced functionality through one or more
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| 53 | extensions, which it installs at identified <b>Extension Points</b>. Each
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| 54 | <b>Addin</b> is characterized by the types of extensions it supplies, so that
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| 55 | an <b>Extension Host</b> knows whether to invoke it.</p>
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| 56 |
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| 57 | <blockquote>
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| 58 | <p><b>Note:</b> In the current release, only Core extensions are actually
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| 59 | supported. An Addin may characterize itself as a Client or Gui extension and
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| 60 | will be listed as such in the <a href="addinsDialog.html">Addins Dialog</a>,
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| 61 | but no other action is taken.</p>
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| 62 | </blockquote>
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| 63 |
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| 64 | <h3>Addin Identification, Loading and Installation</h3>
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| 65 |
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| 66 | <p>NUnit examines all assemblies in the <b>bin/addins</b> directory, looking
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| 67 | for public classes with the <b>NUnitAddinAttribute</b> and implementing the
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| 68 | <b>IAddin</b> interface. It loads all those it finds as Addins.</p>
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| 69 |
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| 70 | <p><b>NUnitAddinAttribute</b> supports three optional named parameters: Type,
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| 71 | Name and Description. Name and Description are strings representing the name
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| 72 | of the extension and a description of what it does. If no name is provided,
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| 73 | the name of the class is used. Type may be any one or a combination of the
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| 74 | ExtensionType enum members:
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| 75 |
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| 76 | <pre>
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| 77 | [Flags]
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| 78 | public enum ExtensionType
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| 79 | {
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| 80 | Core=1,
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| 81 | Client=2,
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| 82 | Gui=4
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| 83 | }
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| 84 | </pre>
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| 85 |
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| 86 | The values may be or'ed together, allowing for future Addins that require
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| 87 | extensions at multiple levels of the application. If not provided, Type
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| 88 | defaults to ExtensionType.Core.</p>
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| 89 |
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| 90 | <p>The <b>IAddin</b> interface, which must be implemented by each Addin,
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| 91 | is defined as follows:</p>
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| 92 |
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| 93 | <pre>
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| 94 | public interface IAddin
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| 95 | {
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| 96 | bool Install( IExtensionHost host );
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| 97 | }
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| 98 | </pre>
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| 99 |
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| 100 | <p> The <b>Install</b> method is called by each host for which the addin has
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| 101 | specified an ExtensionType. The addin should check that the necessary extension
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| 102 | points are available and install itself, returning true for success or false
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| 103 | for failure to install. The method will be called once for each extension
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| 104 | host and - for Core extensions - each time a new test domain is loaded.</p>
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| 105 |
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| 106 | <p>The Install method uses the <b>IExtensionHost</b> interface to locate
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| 107 | extension points. It is defined as follows:</p>
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| 108 |
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| 109 | <pre>
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| 110 | public interface IExtensionHost
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| 111 | {
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| 112 | IExtensionPoint[] ExtensionPoints { get; }
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| 113 | IExtensionPoint GetExtensionPoint( string name );
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| 114 | ExtensionType ExtensionTypes { get; }
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| 115 | }
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| 116 | </pre>
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| 117 |
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| 118 | <p>The <b>ExtensionPoints</b> property returns an array of all extension points
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| 119 | for those extensions that need the information. The <b>ExtensionTypes</b>
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| 120 | property returns the flags for the type of extension supported by this host,
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| 121 | allowing, for example, Gui extensions to only load in a Gui host.</p>
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| 122 |
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| 123 | <p>Most addins will only need to use the <b>GetExtensionPoint</b> method to
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| 124 | get the interface to a particular extension point. The <b>IExtensionPoint</b>
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| 125 | interface is defined as follows:</p>
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| 126 |
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| 127 | <pre>
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| 128 | public interface IExtensionPoint
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| 129 | {
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| 130 | string Name { get; }
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| 131 | IExtensionHost Host { get; }
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| 132 | void Install( object extension );
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| 133 | void Remove( object extension );
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| 134 | }
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| 135 | </pre>
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| 136 |
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| 137 | <p>Once again, most addins will only need to use one method - the
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| 138 | <b>Install</b> method in this case. This method passes an extension object
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| 139 | to the <b>Extension Point</b> where it is installed. Generally, extensions
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| 140 | do not need to remove themselves once installed, but the method is
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| 141 | provided in any case.</p>
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| 142 |
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| 143 | <p>With NUnit 2.5, an additional interface, <b>IExtensionPoint2</b> is
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| 144 | available. It derives from <b>IExtensionPoint</b> and also allows setting
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| 145 | the priority order in which the extension will be called in comparison to
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| 146 | other extensions on the same extension point. The interface is defined
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| 147 | as follows:
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| 148 |
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| 149 | <pre>
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| 150 | public interface IExtensionPoint2 : IExtensionPoint
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| 151 | {
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| 152 | void Install( object extension, int priority );
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| 153 | }
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| 154 | </pre>
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| 155 |
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| 156 | <p>Only extension points that use a priority scheme implement this interface.
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| 157 | In general, extension points with a priority scheme will use a default value
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| 158 | for priority if the Install method without a priority is called.
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| 159 |
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| 160 | <p>In the NUnit 2.5 release, only the <b>TestDecorators</b> extension point implements
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| 161 | <b>IExtensionPoint2</b>.
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| 162 |
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| 163 | <h3>Extension Point Details</h3>
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| 164 |
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| 165 | <p>Depending on the particular extension point, the object passed will
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| 166 | need to implement one or more interfaces. The following <b>ExtensionPoints</b>
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| 167 | are implemented in this release of NUnit:
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| 168 |
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| 169 | <ul>
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| 170 | <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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| 171 |
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| 172 | <p>For examples of implementing each type of extension, see the Extensibility
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| 173 | samples provided with NUnit. More complete examples are available in the
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| 174 | code of NUnit itself, since NUnit uses the same mechanism internally.</p>
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| 175 |
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| 176 | <h4>See also...</h4>
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| 177 |
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| 178 | <ul>
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| 179 | <li><a href="extensionTips.html">Tips for Writing Extensions</a></ul>
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| 218 | Copyright © 2010 Charlie Poole. All Rights Reserved.
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