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<header>
<copyright>
<year>2012</year><year>2015</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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<title>assert.hrl</title>
<prepared></prepared>
<docno></docno>
<date></date>
<rev></rev>
</header>
<file>assert.hrl</file>
<filesummary>Assert Macros</filesummary>
<description>
<p>The include file <c>assert.hrl</c> provides macros for inserting
assertions in your program code.</p>
<p>These macros are defined in the Stdlib include file
<c>assert.hrl</c>. Include the following directive in the module
from which the function is called:</p>
<code type="none">
-include_lib("stdlib/include/assert.hrl").</code>
<p>When an assertion succeeds, the assert macro yields the atom
<c>ok</c>. When an assertion fails, an exception of type <c>error</c> is
instead generated. The associated error term will have the form
<c>{Macro, Info}</c>, where <c>Macro</c> is the name of the macro, for
example <c>assertEqual</c>, and <c>Info</c> will be a list of tagged
values such as <c>[{module, M}, {line, L}, ...]</c> giving more
information about the location and cause of the exception. All entries
in the <c>Info</c> list are optional, and you should not rely
programatically on any of them being present.</p>
<p>If the macro <c>NOASSERT</c> is defined when the <c>assert.hrl</c>
include file is read by the compiler, the macros will be defined as
equivalent to the atom <c>ok</c>. The test will not be performed, and
there will be no cost at runtime.</p>
<p>For example, using <c>erlc</c> to compile your modules, the following
will disable all assertions:</p>
<code type="none">
erlc -DNOASSERT=true *.erl</code>
<p>(The value of <c>NOASSERT</c> does not matter, only the fact that it
is defined.)</p>
<p>A few other macros also have effect on the enabling or disabling of
assertions:</p>
<list type="bulleted">
<item>If <c>NODEBUG</c> is defined, it implies <c>NOASSERT</c>, unless
<c>DEBUG</c> is also defined, which is assumed to take
precedence.</item>
<item>If <c>ASSERT</c> is defined, it overrides <c>NOASSERT</c>, that
is, the assertions will remain enabled.</item>
</list>
<p>If you prefer, you can thus use only <c>DEBUG</c>/<c>NODEBUG</c> as
the main flags to control the behaviour of the assertions (which is
useful if you have other compiler conditionals or debugging macros
controlled by those flags), or you can use <c>ASSERT</c>/<c>NOASSERT</c>
to control only the assert macros.</p>
</description>
<section>
<title>Macros</title>
<taglist>
<tag><c>assert(BoolExpr)</c></tag>
<item><p>Tests that <c>BoolExpr</c> completes normally returning
<c>true</c>.</p>
</item>
<tag><c>assertNot(BoolExpr)</c></tag>
<item><p>Tests that <c>BoolExpr</c> completes normally returning
<c>false</c>.</p>
</item>
<tag><c>assertMatch(GuardedPattern, Expr)</c></tag>
<item><p>Tests that <c>Expr</c> completes normally yielding a value
that matches <c>GuardedPattern</c>. For example:</p>
<code type="none">
?assertMatch({bork, _}, f())</code>
<p>Note that a guard <c>when ...</c> can be included:</p>
<code type="none">
?assertMatch({bork, X} when X > 0, f())</code>
</item>
<tag><c>assertNotMatch(GuardedPattern, Expr)</c></tag>
<item><p>Tests that <c>Expr</c> completes normally yielding a value
that does not match <c>GuardedPattern</c>.</p>
<p>As in <c>assertMatch</c>, <c>GuardedPattern</c> can have a
<c>when</c> part.</p>
</item>
<tag><c>assertEqual(ExpectedValue, Expr)</c></tag>
<item><p>Tests that <c>Expr</c> completes normally yielding a value
that is exactly equal to <c>ExpectedValue</c>.</p>
</item>
<tag><c>assertNotEqual(ExpectedValue, Expr)</c></tag>
<item><p>Tests that <c>Expr</c> completes normally yielding a value
that is not exactly equal to <c>ExpectedValue</c>.</p>
</item>
<tag><c>assertException(Class, Term, Expr)</c></tag>
<item><p>Tests that <c>Expr</c> completes abnormally with an exception
of type <c>Class</c> and with the associated <c>Term</c>. The
assertion fails if <c>Expr</c> raises a different exception or if it
completes normally returning any value.</p>
<p>Note that both <c>Class</c> and <c>Term</c> can be guarded
patterns, as in <c>assertMatch</c>.</p>
</item>
<tag><c>assertNotException(Class, Term, Expr)</c></tag>
<item><p>Tests that <c>Expr</c> does not evaluate abnormally with an
exception of type <c>Class</c> and with the associated <c>Term</c>.
The assertion succeeds if <c>Expr</c> raises a different exception or
if it completes normally returning any value.</p>
<p>As in <c>assertException</c>, both <c>Class</c> and <c>Term</c>
can be guarded patterns.</p>
</item>
<tag><c>assertError(Term, Expr)</c></tag>
<item><p>Equivalent to <c>assertException(error, Term,
Expr)</c></p>
</item>
<tag><c>assertExit(Term, Expr)</c></tag>
<item><p>Equivalent to <c>assertException(exit, Term, Expr)</c></p>
</item>
<tag><c>assertThrow(Term, Expr)</c></tag>
<item><p>Equivalent to <c>assertException(throw, Term, Expr)</c></p>
</item>
</taglist>
</section>
<section>
<title>SEE ALSO</title>
<p><seealso marker="compiler:compile">compile(3)</seealso></p>
<p><seealso marker="erts:erlc">erlc(3)</seealso></p>
</section>
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