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<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE fileref SYSTEM "fileref.dtd">

<fileref>
  <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.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.

    </legalnotice>

    <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>
</fileref>