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| 2 |
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| 3 | <head>
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| 4 | <meta http-equiv="Content-Language" content="en-us">
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| 5 | <title>Assertions type</title>
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| 6 | <link rel="stylesheet" type="text/css" href="../stylesheets/antmanual.css">
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| 7 | </head>
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| 8 |
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| 9 | <body>
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| 10 |
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| 11 | <h2><a name="assertions">Assertions</a></h2>
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| 12 | <p>
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| 13 | The <tt>assertions</tt> type enables or disables the Java 1.4 assertions feature,
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| 14 | on a whole Java program, or components of a program. It can be used
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| 15 | in <a href="../CoreTasks/java.html"><java></a> and
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| 16 | <a href="../OptionalTasks/junit.html"><junit></a> to add extra validation to code.
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| 17 |
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| 18 | <p>
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| 19 | Assertions are covered in the
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| 20 | <a href="http://java.sun.com/j2se/1.4.2/docs/guide/lang/assert.html">J2SDK 1.4 documentation</a>,
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| 21 | and the
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| 22 | <a href="http://java.sun.com/docs/books/jls/assert-spec.html">Java Language Specification</a>.
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| 23 |
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| 24 | <p>
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| 25 | The key points to note are that a <tt>java.lang.AssertionError</tt>
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| 26 | is thrown when an assertion fails, and that the facility is only available
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| 27 | on Java 1.4 and later. To enable assertions one must set <tt>source="1.4"</tt>
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| 28 | (or later) in <tt><javac></tt> when the source is being compiled, and
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| 29 | that the code must contain <tt>assert</tt> statements to be tested. The
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| 30 | result of such an action is code that neither compiles or runs on earlier
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| 31 | versions of Java. For this reason Ant itself currently contains no assertions.
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| 32 | <p>
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| 33 |
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| 34 | When assertions are enabled (or disabled) in a task through nested
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| 35 | assertions elements, the class loader or command line is modified with the
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| 36 | appropriate options. This means that the JVM executed must be a Java 1.4
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| 37 | or later JVM, even if there are no assertions in the code. Attempting to
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| 38 | enable assertions on earlier VMs will result in an "Unrecognized option"
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| 39 | error and the JVM will not start.
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| 40 |
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| 41 | <p>
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| 42 | <h4>Attributes</h4>
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| 43 | <p>
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| 44 |
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| 45 |
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| 46 | </p>
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| 47 | <table border="1" cellpadding="2" cellspacing="0">
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| 48 | <tr>
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| 49 | <td valign="top"><b>Attribute</b></td>
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| 50 | <td valign="top"><b>Description</b></td>
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| 51 | <td align="center" valign="top"><b>Required</b></td>
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| 52 | </tr>
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| 53 | <tr>
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| 54 | <td valign="top">enableSystemAssertions</td>
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| 55 | <td valign="top">Flag to turn system assertions on or off.</td>
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| 56 | <td valign="top" align="center">No; default is "unspecified"</td>
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| 57 | </tr>
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| 58 | </table>
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| 59 | <p>
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| 60 | When system assertions have been neither enabled nor disabled, then
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| 61 | the JVM is not given any assertion information - the default action of the
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| 62 | current JVMs is to disable system assertions.
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| 63 | <p>
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| 64 | Note also that there is no apparent documentation for what parts of the
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| 65 | JRE come with useful assertions.
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| 66 |
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| 67 | <h3>Nested elements</h3>
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| 68 |
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| 69 | <h4>enable</h4>
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| 70 | <p>
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| 71 | Enable assertions in portions of code.
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| 72 | If neither a package nor class is specified, assertions are turned on in <i>all</i> (user) code.
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| 73 | </p>
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| 74 | <table border="1" cellpadding="2" cellspacing="0">
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| 75 | <tr>
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| 76 | <td valign="top"><b>Attribute</b></td>
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| 77 | <td valign="top"><b>Description</b></td>
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| 78 | <td align="center" valign="top"><b>Required</b></td>
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| 79 | </tr>
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| 80 | <tr>
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| 81 | <td valign="top">class</td>
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| 82 | <td valign="top">The name of a class on which to enable assertions.</td>
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| 83 | <td valign="top" align="center">No</td>
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| 84 | </tr>
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| 85 | <tr>
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| 86 | <td valign="top">package</td>
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| 87 | <td valign="top">
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| 88 | The name of a package in which to enable assertions on all classes. (Includes subpackages.)
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| 89 | Use "<tt>...</tt>" for the anonymous package.
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| 90 | </td>
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| 91 | <td valign="top" align="center">No</td>
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| 92 | </tr>
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| 93 | </table>
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| 94 |
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| 95 | <h4>disable</h4>
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| 96 | <p>
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| 97 | Disable assertions in portions of code.
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| 98 |
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| 99 | </p>
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| 100 | <table border="1" cellpadding="2" cellspacing="0">
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| 101 | <tr>
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| 102 | <td valign="top"><b>Attribute</b></td>
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| 103 | <td valign="top"><b>Description</b></td>
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| 104 | <td align="center" valign="top"><b>Required</b></td>
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| 105 | </tr>
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| 106 | <tr>
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| 107 | <td valign="top">class</td>
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| 108 | <td valign="top">The name of a class on which to disable assertions.</td>
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| 109 | <td valign="top" align="center">No</td>
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| 110 | </tr>
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| 111 | <tr>
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| 112 | <td valign="top">package</td>
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| 113 | <td valign="top">
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| 114 | The name of a package in which to disable assertions on all classes. (Includes subpackages.)
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| 115 | Use "<tt>...</tt>" for the anonymous package.
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| 116 | </td>
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| 117 | <td valign="top" align="center">No</td>
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| 118 | </tr>
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| 119 | </table>
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| 120 | <p>
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| 121 |
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| 122 | Because assertions are disabled by default, it only makes sense to disable
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| 123 | assertions where they have been enabled in a parent package.
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| 124 |
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| 125 |
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| 126 | <h4>Examples</h4>
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| 127 |
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| 128 | <h5>Example: enable assertions in all user classes</h5>
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| 129 |
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| 130 | All classes not in the JRE (i.e. all non-system classes) will have assertions turned on.
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| 131 | <pre>
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| 132 | <assertions>
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| 133 | <enable/>
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| 134 | </assertions>
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| 135 | </pre>
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| 136 |
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| 137 | <h5>Example: enable a single class</h5>
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| 138 |
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| 139 | Enable assertions in a class called Test
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| 140 | <pre>
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| 141 | <assertions>
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| 142 | <enable class="Test"/>
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| 143 | </assertions>
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| 144 | </pre>
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| 145 |
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| 146 | <h5>Example: enable a package</h5>
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| 147 |
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| 148 | Enable assertions in the <tt>org.apache</tt> package
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| 149 | and all packages starting with the <tt>org.apache.</tt> prefix
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| 150 | <pre>
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| 151 | <assertions>
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| 152 | <enable package="org.apache"/>
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| 153 | </assertions>
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| 154 | </pre>
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| 155 |
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| 156 | <h5>Example: System assertions</h5>
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| 157 |
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| 158 | Example: enable system assertions and assertions in all <tt>org.apache</tt> packages except
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| 159 | for Ant (but including <tt>org.apache.tools.ant.Main</tt>)
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| 160 | <pre>
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| 161 | <assertions enableSystemAssertions="true">
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| 162 | <enable package="org.apache"/>
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| 163 | <disable package="org.apache.tools.ant"/>
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| 164 | <enable class="org.apache.tools.ant.Main"/>
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| 165 | </assertions>
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| 166 | </pre>
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| 167 |
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| 168 | <h5>Example: disabled and anonymous package assertions</h5>
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| 169 |
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| 170 | Disable system assertions; enable those in the anonymous package
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| 171 | <pre>
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| 172 | <assertions enableSystemAssertions="false">
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| 173 | <enable package="..."/>
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| 174 | </assertions>
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| 175 | </pre>
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| 176 |
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| 177 |
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| 178 | <h5>Example: referenced assertions</h5>
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| 179 |
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| 180 | This type is a datatype, so you can declare assertions and use them later
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| 181 |
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| 182 | <pre>
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| 183 | <assertions id="project.assertions">
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| 184 | <enable package="org.apache.test"/>
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| 185 | </assertions>
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| 186 |
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| 187 | <assertions refid="project.assertions"/>
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| 188 | </pre>
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| 189 |
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| 190 | <hr>
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| 191 | <p align="center">Copyright © 2003-2004 The Apache Software Foundation. All rights
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| 192 | Reserved.</p>
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| 193 | </body>
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| 194 | </html>
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