1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>BOOST_TEST: details on expressions</title> 5<link rel="stylesheet" href="../../boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../index.html" title="Boost.Test"> 8<link rel="up" href="../testing_tools.html" title="Writing unit tests"> 9<link rel="prev" href="output_stream_testing.html" title="Output streams testing tool"> 10<link rel="next" href="debugging.html" title="Debugging the assertions"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> 17<td 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class="computeroutput"><span class="identifier">BOOST_TEST</span></code>: details on expressions</a> 28</h3></div></div></div> 29<p> 30 Let's consider the following example: 31 </p> 32<h6> 33<a name="boost_test.testing_tools.internal_details.h0"></a> 34 <span class="phrase"><a name="boost_test.testing_tools.internal_details.example_descr"></a></span><a class="link" href="internal_details.html#boost_test.testing_tools.internal_details.example_descr">Example: 35 BOOST_TEST reporting</a> 36 </h6> 37<div class="informaltable"><table class="table"> 38<colgroup><col></colgroup> 39<thead><tr><th> 40 <p> 41 Code 42 </p> 43 </th></tr></thead> 44<tbody><tr><td> 45<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="preprocessor">#define</span> <span class="identifier">BOOST_TEST_MODULE</span> <span class="identifier">boost_test_macro3</span> 46<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">test</span><span class="special">/</span><span class="identifier">included</span><span class="special">/</span><span class="identifier">unit_test</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 47 48<span class="identifier">BOOST_AUTO_TEST_CASE</span><span class="special">(</span> <span class="identifier">test_op_reportings</span> <span class="special">)</span> 49<span class="special">{</span> 50 <span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">13</span><span class="special">,</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">12</span><span class="special">;</span> 51 <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">a</span> <span class="special">==</span> <span class="identifier">b</span><span class="special">);</span> 52 <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">a</span> <span class="special"><</span> <span class="identifier">b</span><span class="special">);</span> 53 <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">a</span> <span class="special">-</span> <span class="number">1</span> <span class="special"><</span> <span class="identifier">b</span><span class="special">);</span> 54 <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">b</span> <span class="special">></span> <span class="identifier">a</span> <span class="special">-</span> <span class="number">1</span><span class="special">);</span> 55<span class="special">}</span> 56</pre> 57 </td></tr></tbody> 58</table></div> 59<div class="informaltable"><table class="table"> 60<colgroup><col></colgroup> 61<thead><tr><th> 62 <p> 63 Output 64 </p> 65 </th></tr></thead> 66<tbody><tr><td> 67<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="special">></span> <span class="special">./</span><span class="identifier">boost_test_macro3</span> <span class="special">--</span><span class="identifier">log_level</span><span class="special">=</span><span class="identifier">all</span> 68<span class="identifier">Running</span> <span class="number">1</span> <span class="identifier">test</span> <span class="keyword">case</span><span class="special">...</span> 69<span class="identifier">Entering</span> <span class="identifier">test</span> <span class="identifier">module</span> <span class="string">"boost_test_macro3"</span> 70<span class="identifier">test</span><span class="special">.</span><span class="identifier">cpp</span><span class="special">(</span><span class="number">12</span><span class="special">):</span> <span class="identifier">Entering</span> <span class="identifier">test</span> <span class="keyword">case</span> <span class="string">"test_op_reportings"</span> 71<span class="identifier">test</span><span class="special">.</span><span class="identifier">cpp</span><span class="special">(</span><span class="number">15</span><span class="special">):</span> <span class="identifier">error</span><span class="special">:</span> <span class="identifier">in</span> <span class="string">"test_op_reportings"</span><span class="special">:</span> <span class="identifier">check</span> <span class="identifier">a</span> <span class="special">==</span> <span class="identifier">b</span> <span class="identifier">has</span> <span class="identifier">failed</span> <span class="special">[</span><span class="number">13</span> <span class="special">!=</span> <span class="number">12</span><span class="special">]</span> 72<span class="identifier">test</span><span class="special">.</span><span class="identifier">cpp</span><span class="special">(</span><span class="number">16</span><span class="special">):</span> <span class="identifier">error</span><span class="special">:</span> <span class="identifier">in</span> <span class="string">"test_op_reportings"</span><span class="special">:</span> <span class="identifier">check</span> <span class="identifier">a</span> <span class="special"><</span> <span class="identifier">b</span> <span class="identifier">has</span> <span class="identifier">failed</span> <span class="special">[</span><span class="number">13</span> <span class="special">>=</span> <span class="number">12</span><span class="special">]</span> 73<span class="identifier">test</span><span class="special">.</span><span class="identifier">cpp</span><span class="special">(</span><span class="number">17</span><span class="special">):</span> <span class="identifier">error</span><span class="special">:</span> <span class="identifier">in</span> <span class="string">"test_op_reportings"</span><span class="special">:</span> <span class="identifier">check</span> <span class="identifier">a</span> <span class="special">-</span> <span class="number">1</span> <span class="special"><</span> <span class="identifier">b</span> <span class="identifier">has</span> <span class="identifier">failed</span> <span class="special">[</span><span class="number">13</span> <span class="special">-</span> <span class="number">1</span> <span class="special">>=</span> <span class="number">12</span><span class="special">]</span> 74<span class="identifier">test</span><span class="special">.</span><span class="identifier">cpp</span><span class="special">(</span><span class="number">18</span><span class="special">):</span> <span class="identifier">error</span><span class="special">:</span> <span class="identifier">in</span> <span class="string">"test_op_reportings"</span><span class="special">:</span> <span class="identifier">check</span> <span class="identifier">b</span> <span class="special">></span> <span class="identifier">a</span> <span class="special">-</span> <span class="number">1</span> <span class="identifier">has</span> <span class="identifier">failed</span> <span class="special">[</span><span class="number">12</span> <span class="special"><=</span> <span class="number">12</span><span class="special">]</span> 75<span class="identifier">test</span><span class="special">.</span><span class="identifier">cpp</span><span class="special">(</span><span class="number">12</span><span class="special">):</span> <span class="identifier">Leaving</span> <span class="identifier">test</span> <span class="keyword">case</span> <span class="string">"test_op_reportings"</span><span class="special">;</span> <span class="identifier">testing</span> <span class="identifier">time</span><span class="special">:</span> <span class="number">484u</span><span class="identifier">s</span> 76<span class="identifier">Leaving</span> <span class="identifier">test</span> <span class="identifier">module</span> <span class="string">"boost_test_macro3"</span><span class="special">;</span> <span class="identifier">testing</span> <span class="identifier">time</span><span class="special">:</span> <span class="number">588u</span><span class="identifier">s</span> 77 78<span class="special">***</span> <span class="number">2</span> <span class="identifier">failures</span> <span class="identifier">are</span> <span class="identifier">detected</span> <span class="identifier">in</span> <span class="identifier">the</span> <span class="identifier">test</span> <span class="identifier">module</span> <span class="string">"boost_test_macro3"</span> 79</pre> 80 </td></tr></tbody> 81</table></div> 82<p> 83 It was already mentioned that the reporting is not symmetrical (see <a class="link" href="reports.html" title="Reported information">here</a>). An expression is 84 constructed from the <code class="computeroutput"><span class="identifier">statement</span></code> 85 appearing in the <code class="computeroutput"><span class="identifier">BOOST_TEST</span></code> 86 macro. This expression allows evaluation and reporting such as <code class="computeroutput"><span class="string">"13 - 1 >= 12"</span> <span class="identifier">failed</span></code> 87 along with a copy of the <code class="computeroutput"><span class="identifier">statement</span></code>, 88 which contains more details than <code class="computeroutput"><span class="string">"a - 1 89 < b"</span> <span class="identifier">failed</span></code>. In 90 details, what happens is the following: 91 </p> 92<div class="orderedlist"><ol class="orderedlist" type="1"> 93<li class="listitem"> 94<p class="simpara"> 95 a special object, the <code class="computeroutput"><span class="identifier">seed</span></code> 96 of the expression, is composed from the left side of <code class="computeroutput"><span class="identifier">statement</span></code>. 97 This initial composition has highest precedence over the supported operations. 98 The expression below: 99 </p> 100<pre class="programlisting"><span class="identifier">a</span> <span class="identifier">op1</span> <span class="identifier">b</span> <span class="identifier">op2</span> <span class="identifier">c</span> <span class="identifier">op3</span> <span class="identifier">d</span> 101</pre> 102<p class="simpara"> 103 is actually seen as 104 </p> 105<pre class="programlisting"><span class="special">(</span> <span class="identifier">seed</span> <span class="identifier">a</span> <span class="special">)</span> <span class="identifier">op1</span> <span class="identifier">b</span> <span class="identifier">op2</span> <span class="identifier">c</span> <span class="identifier">op3</span> <span class="identifier">d</span> 106</pre> 107</li> 108<li class="listitem"> 109<p class="simpara"> 110 The "<code class="computeroutput"><span class="identifier">seed</span> <span class="identifier">a</span></code>" 111 returns an <code class="computeroutput"><span class="identifier">expression</span></code> 112 object that keep tracks of the type of <code class="computeroutput"><span class="identifier">a</span></code>. 113 This expression has overloads for left-to-right associativity, and the 114 operations <code class="computeroutput"><span class="identifier">op1</span></code>, <code class="computeroutput"><span class="identifier">op2</span></code> ... are <span class="emphasis"><em>chained</em></span> 115 to the right of this expression object: 116 </p> 117<pre class="programlisting"><span class="identifier">a</span> <span class="identifier">op1</span> <span class="identifier">b</span> 118</pre> 119<p class="simpara"> 120 yields to the pseudo-code 121 </p> 122<pre class="programlisting"><span class="identifier">expression1</span> <span class="special">=</span> <span class="identifier">create</span><span class="special">-</span><span class="identifier">expression</span><span class="special">(</span><span class="identifier">a</span><span class="special">)</span> 123<span class="identifier">expression2</span> <span class="special">=</span> <span class="identifier">create</span><span class="special">-</span><span class="identifier">expression</span><span class="special">(</span><span class="identifier">expression1</span><span class="special">,</span> <span class="identifier">op1</span><span class="special">,</span> <span class="identifier">b</span><span class="special">)</span> 124</pre> 125<p class="simpara"> 126 <code class="computeroutput"><span class="identifier">expression1</span></code> and <code class="computeroutput"><span class="identifier">expression2</span></code> keep track of their left 127 and right operands, and the operation on those operands. The expressions 128 keep also track of the result type of the associated sub-expression. 129 In the above example, <code class="computeroutput"><span class="identifier">expression1</span></code> 130 and <code class="computeroutput"><span class="identifier">expression2</span></code> have 131 result type <code class="computeroutput"><span class="keyword">decltype</span><span class="special">(</span><span class="identifier">a</span><span class="special">)</span></code> 132 and <code class="computeroutput"><span class="keyword">decltype</span><span class="special">(</span><span class="identifier">a</span> <span class="identifier">op1</span> 133 <span class="identifier">b</span><span class="special">)</span></code> 134 respectively. The result type allows for chaining sub-expressions. 135 </p> 136</li> 137<li class="listitem"> 138<p class="simpara"> 139 The C++ operators precedence rules apply in any case. What is seen by 140 the expression is what is reachable with left-to-right composition. Any 141 other operation that happens before it reaches the expression's right 142 operand is not parsed as a sub-expression and is seen as a single operand: 143 the right operand is not developed further by the framework. Let's suppose 144 <code class="computeroutput"><span class="identifier">op2</span></code> below has higher 145 precedence than <code class="computeroutput"><span class="identifier">op1</span></code>, 146 then 147 </p> 148<pre class="programlisting"><span class="identifier">a</span> <span class="identifier">op1</span> <span class="identifier">b</span> <span class="identifier">op2</span> <span class="identifier">c</span> 149</pre> 150<p class="simpara"> 151 is equivalent to: 152 </p> 153<pre class="programlisting"><span class="identifier">create</span><span class="special">-</span><span class="identifier">expression</span><span class="special">(</span><span class="identifier">create</span><span class="special">-</span><span class="identifier">expression</span><span class="special">(</span><span class="identifier">a</span><span class="special">),</span> <span class="identifier">op1</span><span class="special">,</span> <span class="special">(</span><span class="identifier">b</span> <span class="identifier">op2</span> <span class="identifier">c</span><span class="special">))</span> 154</pre> 155<p class="simpara"> 156 In the above statement, the final expression can only see the result 157 of <code class="computeroutput"><span class="special">(</span><span class="identifier">b</span> 158 <span class="identifier">op2</span> <span class="identifier">c</span><span class="special">)</span></code> to its right, for which no further detail 159 can be provided in the logs. This is also the case for <span class="emphasis"><em>right-to-left</em></span> 160 associative operators, such as <code class="computeroutput"><span class="special">!</span></code>, 161 <code class="computeroutput"><span class="special">~</span></code>, <code class="computeroutput"><span class="special">-</span></code> 162 (unary negation) etc. 163 </p> 164<div class="caution"><table border="0" summary="Caution"> 165<tr> 166<td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../../../../../../doc/src/images/caution.png"></td> 167<th align="left">Caution</th> 168</tr> 169<tr><td align="left" valign="top"><p> 170 Since the <code class="computeroutput"><span class="identifier">expression</span></code> 171 object is composed from left-to-right, it actually observes a chain 172 of operations and not the full expression tree. 173 </p></td></tr> 174</table></div> 175</li> 176<li class="listitem"> 177<p class="simpara"> 178 Once the full expression chain is built, it is evaluated as a chain of 179 sub-expressions from left-to-right, exactly as the composition rule above. 180 The evaluated elements are the ones of the expression itself. The expression 181 </p> 182<pre class="programlisting"><span class="identifier">a</span> <span class="identifier">op1</span> <span class="identifier">b</span> 183</pre> 184<p class="simpara"> 185 yields to the following evaluation chain: 186 </p> 187<pre class="programlisting"><span class="identifier">expression2</span><span class="special">.</span><span class="identifier">result</span> <span class="special">=</span> <span class="identifier">expression1</span><span class="special">.</span><span class="identifier">result</span> <span class="identifier">op1</span> <span class="identifier">b</span> 188<span class="identifier">expression1</span><span class="special">.</span><span class="identifier">result</span> <span class="special">=</span> <span class="identifier">a</span> 189</pre> 190<p class="simpara"> 191 The final expression of the statement is cast to a boolean, which is 192 in turn evaluated by the <span class="emphasis"><em>Unit Test Framework</em></span>. 193 </p> 194</li> 195</ol></div> 196<p> 197 The example below illustrates the construction of the left-to-right <span class="emphasis"><em>chained</em></span> 198 expression. 199 </p> 200<h6> 201<a name="boost_test.testing_tools.internal_details.h1"></a> 202 <span class="phrase"><a name="boost_test.testing_tools.internal_details.example_descr0"></a></span><a class="link" href="internal_details.html#boost_test.testing_tools.internal_details.example_descr0">Example: 203 BOOST_TEST compound statements</a> 204 </h6> 205<div class="informaltable"><table class="table"> 206<colgroup><col></colgroup> 207<thead><tr><th> 208 <p> 209 Code 210 </p> 211 </th></tr></thead> 212<tbody><tr><td> 213<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="preprocessor">#define</span> <span class="identifier">BOOST_TEST_MODULE</span> <span class="identifier">boost_test_macro2</span> 214<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">test</span><span class="special">/</span><span class="identifier">included</span><span class="special">/</span><span class="identifier">unit_test</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 215 216<span class="identifier">BOOST_AUTO_TEST_CASE</span><span class="special">(</span> <span class="identifier">test_op_precedence</span> <span class="special">)</span> 217<span class="special">{</span> 218 <span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">13</span><span class="special">,</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span><span class="special">,</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">12</span><span class="special">;</span> 219 <span class="comment">// left term of == is expanded in the logs</span> 220 <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">a</span> <span class="special">%</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">c</span><span class="special">);</span> 221 <span class="comment">// right term of == is not expanded in the logs</span> 222 <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">a</span> <span class="special">==</span> <span class="identifier">c</span> <span class="special">%</span> <span class="identifier">b</span><span class="special">);</span> 223<span class="special">}</span> 224 225<span class="identifier">BOOST_AUTO_TEST_CASE</span><span class="special">(</span> <span class="identifier">test_op_right_associative</span> <span class="special">)</span> 226<span class="special">{</span> 227 <span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> 228 <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">a</span><span class="special">);</span> 229 <span class="identifier">BOOST_TEST</span><span class="special">(!</span><span class="identifier">a</span><span class="special">);</span> 230 <span class="identifier">BOOST_TEST</span><span class="special">(--</span><span class="identifier">a</span><span class="special">);</span> 231<span class="special">}</span> 232</pre> 233 </td></tr></tbody> 234</table></div> 235<div class="informaltable"><table class="table"> 236<colgroup><col></colgroup> 237<thead><tr><th> 238 <p> 239 Output 240 </p> 241 </th></tr></thead> 242<tbody><tr><td> 243<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="special">></span> <span class="special">./</span><span class="identifier">boost_test_macro2</span> <span class="special">--</span><span class="identifier">log_level</span><span class="special">=</span><span class="identifier">all</span> 244<span class="identifier">Running</span> <span class="number">2</span> <span class="identifier">test</span> <span class="identifier">cases</span><span class="special">...</span> 245<span class="identifier">test</span><span class="special">.</span><span class="identifier">cpp</span><span class="special">(</span><span class="number">16</span><span class="special">):</span> <span class="identifier">error</span><span class="special">:</span> <span class="identifier">in</span> <span class="string">"test_op_precedence"</span><span class="special">:</span> <span class="identifier">check</span> <span class="identifier">a</span> <span class="special">%</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">c</span> <span class="identifier">has</span> <span class="identifier">failed</span> <span class="special">[</span><span class="number">13</span> <span class="special">%</span> <span class="number">2</span> <span class="special">!=</span> <span class="number">12</span><span class="special">]</span> 246<span class="identifier">test</span><span class="special">.</span><span class="identifier">cpp</span><span class="special">(</span><span class="number">18</span><span class="special">):</span> <span class="identifier">error</span><span class="special">:</span> <span class="identifier">in</span> <span class="string">"test_op_precedence"</span><span class="special">:</span> <span class="identifier">check</span> <span class="identifier">a</span> <span class="special">==</span> <span class="identifier">c</span> <span class="special">%</span> <span class="identifier">b</span> <span class="identifier">has</span> <span class="identifier">failed</span> <span class="special">[</span><span class="number">13</span> <span class="special">!=</span> <span class="number">0</span><span class="special">]</span> 247<span class="identifier">test</span><span class="special">.</span><span class="identifier">cpp</span><span class="special">(</span><span class="number">25</span><span class="special">):</span> <span class="identifier">error</span><span class="special">:</span> <span class="identifier">in</span> <span class="string">"test_op_right_associative"</span><span class="special">:</span> <span class="identifier">check</span> <span class="special">!</span><span class="identifier">a</span> <span class="identifier">has</span> <span class="identifier">failed</span> 248<span class="identifier">test</span><span class="special">.</span><span class="identifier">cpp</span><span class="special">(</span><span class="number">26</span><span class="special">):</span> <span class="identifier">error</span><span class="special">:</span> <span class="identifier">in</span> <span class="string">"test_op_right_associative"</span><span class="special">:</span> <span class="identifier">check</span> <span class="special">--</span><span class="identifier">a</span> <span class="identifier">has</span> <span class="identifier">failed</span> <span class="special">[(</span><span class="keyword">bool</span><span class="special">)</span><span class="number">0</span> <span class="identifier">is</span> <span class="keyword">false</span><span class="special">]</span> 249 250<span class="special">***</span> <span class="number">4</span> <span class="identifier">failures</span> <span class="identifier">are</span> <span class="identifier">detected</span> <span class="identifier">in</span> <span class="identifier">the</span> <span class="identifier">test</span> <span class="identifier">module</span> <span class="string">"boost_test_macro2"</span> 251</pre> 252 </td></tr></tbody> 253</table></div> 254</div> 255<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 256<td align="left"></td> 257<td align="right"><div class="copyright-footer">Copyright © 2001-2020 Boost.Test contributors<p> 258 Distributed under the Boost Software License, Version 1.0. (See accompanying 259 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 260 </p> 261</div></td> 262</tr></table> 263<hr> 264<div class="spirit-nav"> 265<a accesskey="p" href="output_stream_testing.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../testing_tools.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="debugging.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 266</div> 267</body> 268</html> 269
