path: root/lib/common_test/doc/src/write_test_chapter.xml

<?xml version="1.0" encoding="latin1" ?>
<!DOCTYPE chapter SYSTEM "chapter.dtd">

<chapter>
  <header>
    <copyright>
      <year>2003</year><year>2010</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
      compliance with the License. You should have received a copy of the
      Erlang Public License along with this software. If not, it can be
      retrieved online at http://www.erlang.org/.

      Software distributed under the License is distributed on an "AS IS"
      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
      the License for the specific language governing rights and limitations
      under the License.

    </legalnotice>

    <title>Writing Test Suites</title>
    <prepared>Siri Hansen, Peter Andersson</prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
    <file>write_test_chapter.xml</file>
  </header>
         

  <section>
    <marker id="intro"></marker>
    <title>Support for test suite authors</title>

    <p>The <c>ct</c> module provides the main interface for writing
    test cases. This includes e.g:</p>

    <list>
      <item>Functions for printing and logging</item>
      <item>Functions for reading configuration data</item>
      <item>Function for terminating a test case with error reason</item>
      <item>Function for adding comments to the HTML overview page</item>
    </list>

    <p>Please see the reference manual for the <c>ct</c>
      module for details about these functions.</p>
    
    <p>The CT application also includes other modules named 
      <c><![CDATA[ct_<something>]]></c> that
      provide various support, mainly simplified use of communication
      protocols such as rpc, snmp, ftp, telnet, etc.</p>

  </section>

  <section>
    <title>Test suites</title>
    
    <p>A test suite is an ordinary Erlang module that contains test
      cases. It is recommended that the module has a name on the form
      <c>*_SUITE.erl</c>. Otherwise, the directory and auto compilation 
      function in CT will not be able to locate it (at least not per default).
    </p>

    <p>The <c>ct.hrl</c> header file must be included in all test suite files.
    </p>

    <p>Each test suite module must export the function <c>all/0</c>
      which returns the list of all test case groups and test cases 
      in that module. 
    </p>

  </section>

  <section>
    <title>Init and end per suite</title>

    <p>Each test suite module may contain the optional configuration functions
    <c>init_per_suite/1</c> and <c>end_per_suite/1</c>. If the init function
    is defined, so must the end function be.
    </p>    

    <p>If it exists, <c>init_per_suite</c> is called initially before the
    test cases are executed. It typically contains initializations that are
    common for all test cases in the suite, and that are only to be
    performed once. It is recommended to be used for setting up and
    verifying state and environment on the SUT (System Under Test) and/or
    the CT host node, so that the test cases in the suite will execute
    correctly. Examples of initial configuration operations: Opening a connection
    to the SUT, initializing a database, running an installation script, etc.
    </p>

    <p><c>end_per_suite</c> is called as the final stage of the test suite execution
    (after the last test case has finished). The function is meant to be used 
    for cleaning up after <c>init_per_suite</c>. 
    </p>
    
    <p><c>init_per_suite</c> and <c>end_per_suite</c> will execute on dedicated
    Erlang processes, just like the test cases do. The result of these functions
    is however not included in the test run statistics of successful, failed and
    skipped cases.
    </p>

    <p>The argument to <c>init_per_suite</c> is <c>Config</c>, the
    same key-value list of runtime configuration data that each test case takes
    as input argument. <c>init_per_suite</c> can modify this parameter with 
    information that the test cases need. The possibly modified <c>Config</c>
    list is the return value of the function.
    </p>

    <p>If <c>init_per_suite</c> fails, all test cases in the test
    suite will be skipped automatically (so called <em>auto skipped</em>), 
    including <c>end_per_suite</c>.
    </p>
  </section>

  <section>
    <title>Init and end per test case</title>

    <p>Each test suite module can contain the optional configuration functions
    <c>init_per_testcase/2</c> and <c>end_per_testcase/2</c>. If the init function
    is defined, so must the end function be.</p>

    <p>If it exists, <c>init_per_testcase</c> is called before each
    test case in the suite. It typically contains initialization which
    must be done for each test case (analogue to <c>init_per_suite</c> for the 
    suite).</p>

    <p><c>end_per_testcase/2</c> is called after each test case has
    finished, giving the opportunity to perform clean-up after 
    <c>init_per_testcase</c>.</p>

    <p>The first argument to these functions is the name of the test
    case. This value can be used with pattern matching in function clauses
    or conditional expressions to choose different initialization and cleanup
    routines for different test cases, or perform the same routine for a number of,
    or all, test cases.</p>

    <p>The second argument is the <c>Config</c> key-value list of runtime
    configuration data, which has the same value as the list returned by
    <c>init_per_suite</c>. <c>init_per_testcase/2</c> may modify this
    parameter or return it as is. The return value of <c>init_per_testcase/2</c> 
    is passed as the <c>Config</c> parameter to the test case itself.</p>
	  
    <p>The return value of <c>end_per_testcase/2</c> is ignored by the
    test server, with exception of the 
    <seealso marker="dependencies_chapter#save_config">save_config</seealso>
    and <c>fail</c> tuple.</p>

    <p>It is possible in <c>end_per_testcase</c> to check if the
      test case was successful or not (which consequently may determine 
      how cleanup should be performed). This is done by reading the value
      tagged with <c>tc_status</c> from <c>Config</c>. The value is either
      <c>ok</c>, <c>{failed,Reason}</c> (where <c>Reason</c> is <c>timetrap_timeout</c>, 
      info from <c>exit/1</c>, or details of a run-time error), or 
      <c>{skipped,Reason}</c> (where Reason is a user specific term).
    </p>

    <p>The <c>end_per_testcase/2</c> function is called even after a
      test case terminates due to a call to <c>ct:abort_current_testcase/1</c>,
      or after a timetrap timeout. However, <c>end_per_testcase</c>
      will then execute on a different process than the test case
      function, and in this situation, <c>end_per_testcase</c> will
      not be able to change the reason for test case termination by
      returning <c>{fail,Reason}</c>, nor will it be able to save data with
      <c>{save_config,Data}</c>.</p>

    <p>If <c>init_per_testcase</c> crashes, the test case itself is skipped 
    automatically (so called <em>auto skipped</em>). If <c>init_per_testcase</c>
    returns a <c>skip</c> tuple, also then will the test case be skipped (so
    called <em>user skipped</em>). In either event, the <c>end_per_testcase</c> is 
    never called.
    </p>

    <p>If it is determined during execution of <c>end_per_testcase</c> that
    the status of a successful test case should be changed to failed, 
    <c>end_per_testcase</c> may return the tuple: <c>{fail,Reason}</c>
    (where <c>Reason</c> describes why the test case fails).</p>

    <p><c>init_per_testcase</c> and <c>end_per_testcase</c> execute on the
    same Erlang process as the test case and printouts from these
    configuration functions can be found in the test case log file.</p>
  </section>

  <section>
    <marker id="test_cases"></marker>
    <title>Test cases</title>
    
    <p>The smallest unit that the test server is concerned with is a
      test case. Each test case can actually test many things, for
      example make several calls to the same interface function with
      different parameters.
    </p>
      
    <p>It is possible to choose to put many or few tests into each test
      case. What exactly each test case does is of course up to the 
      author, but here are some things to keep in mind:
    </p>      

    <p>Having many small test cases tend to result in extra, and possibly
      duplicated code, as well as slow test execution because of
      large overhead for initializations and cleanups. Duplicated 
      code should be avoided, e.g. by means of common help functions, or
      the resulting suite will be difficult to read and understand, and
      expensive to maintain.
    </p>

    <p>Larger test cases make it harder to tell what went wrong if it
      fails, and large portions of test code will potentially be skipped
      when errors occur. Furthermore, readability and maintainability suffers 
      when test cases become too large and extensive. Also, the resulting log
      files may not reflect very well the number of tests that have
      actually been performed.
    </p>

    <p>The test case function takes one argument, <c>Config</c>, which
      contains configuration information such as <c>data_dir</c> and
      <c>priv_dir</c>. (See <seealso marker="#data_priv_dir">Data and
	Private Directories</seealso> for more information about these).
	The value of <c>Config</c> at the time of the call, is the same 
	as the return value from <c>init_per_testcase</c>, see above.
    </p>

    <note><p>The test case function argument <c>Config</c> should not be 
	confused with the information that can be retrieved from 
	configuration files (using ct:get_config/[1,2]). The Config argument 
	should be used for runtime configuration of the test suite and the 
	test cases, while configuration files should typically contain data 
	related to the SUT. These two types of configuration data are handled 
	differently!</p></note>
    
    <p>Since the <c>Config</c> parameter is a list of key-value tuples, i.e.
    a data type generally called a property list, it can be handled by means of the
    <c>proplists</c> module in the OTP <c>stdlib</c>. A value can for example
    be searched for and returned with the <c>proplists:get_value/2</c> function.
    Also, or alternatively, you might want to look in the general <c>lists</c> module,
    also in <c>stdlib</c>, for useful functions. Normally, the only operations you
    ever perform on <c>Config</c> is insert (adding a tuple to the head of the list) 
    and lookup. Common Test provides a simple macro named <c>?config</c>, which returns 
    a value of an item in <c>Config</c> given the key (exactly like 
    <c>proplists:get_value</c>). Example: <c>PrivDir = ?config(priv_dir, Config)</c>.
    </p>

    <p>If the test case function crashes or exits purposely, it is considered 
    <em>failed</em>. If it returns a value (no matter what actual value) it is 
    considered successful. An exception to this rule is the return value 
    <c>{skip,Reason}</c>. If this tuple is returned, the test case is considered 
    skipped and gets logged as such.</p> 

    <p>If the test case returns the tuple <c>{comment,Comment}</c>, the case
    is considered successful and <c>Comment</c> is printed out in the overview 
    log file. This is by the way equal to calling <c>ct:comment(Comment)</c>.
    </p>

  </section>

  <section>
    <marker id="info_function"></marker>
      <title>Test case info function</title>
      
      <p>For each test case function there can be an additional function
	with the same name but with no arguments. This is the test case
	info function. The test case info function is expected to return a 
	list of	tagged tuples that specifies various properties regarding the 
	test case.
      </p>
      
      <p>The following tags have special meaning:</p>
      <taglist>
	<tag><em><c>timetrap</c></em></tag>
	<item>
	  <p>
	    Set the maximum time the test case is allowed to execute. If
	    the timetrap time is exceeded, the test case fails with
	    reason <c>timetrap_timeout</c>. Note that <c>init_per_testcase</c> 
	    and <c>end_per_testcase</c> are included in the timetrap time.
	  </p>
	</item>
	<tag><em><c>userdata</c></em></tag>
	<item>
	  <p>
	    Use this to specify arbitrary data related to the testcase. This
	    data can be retrieved at any time using the <c>ct:userdata/3</c> 
	    utility function.
	  </p>
	</item>
	<tag><em><c>silent_connections</c></em></tag>
	<item>
	  <p>
	    Please see the 
	    <seealso marker="run_test_chapter#silent_connections">Silent Connections</seealso>
	    chapter for details.
	  </p>
	</item>
	<tag><em><c>require</c></em></tag>
	<item>
	  <p>
	    Use this to specify configuration variables that are required by the
	    test case. If the required configuration variables are not
	    found in any of the test system configuration files, the test case is
	    skipped.</p> 
	  <p>
	    It is also possible to give a required variable a default value that will 
	    be used if the variable is not found in any configuration file. To specify 
	    a default value, add a tuple on the form: 
	    <c>{default_config,ConfigVariableName,Value}</c> to the test case info list 
	    (the position in the list is irrelevant).
	    Examples:</p>
      
	  <pre>
	    testcase1() -> 
	        [{require, ftp},
	         {default_config, ftp, [{ftp, "my_ftp_host"},
	                                {username, "aladdin"},
	                                {password, "sesame"}]}}].</pre>

	  <pre>
	    testcase2() -> 
	        [{require, unix_telnet, {unix, [telnet, username, password]}},
	         {default_config, unix, [{telnet, "my_telnet_host"},
	                                 {username, "aladdin"},
	                                 {password, "sesame"}]}}].</pre>
	</item>
      </taglist>

	<p>See the <seealso marker="config_file_chapter#require_config_data">Config files</seealso>
	  chapter and the <c>ct:require/[1,2]</c> function in the
	   <seealso marker="ct">ct</seealso> reference manual for more information about
	   <c>require</c>.</p>

      <note><p>Specifying a default value for a required variable can result
	  in a test case always getting executed. This might not be a desired behaviour!</p>
      </note>  
    
      <p>If <c>timetrap</c> and/or <c>require</c> is not set specifically for
	a particular test case, default values specified by the <c>suite/0</c> 
	function are used.
      </p>

      <p>Other tags than the ones mentioned above will simply be ignored by
	the test server.
      </p>

      <p>
	Example of a test case info function:
      </p>
      <pre>
	reboot_node() ->
	    [
	     {timetrap,{seconds,60}},
	     {require,interfaces},
	     {userdata,
	         [{description,"System Upgrade: RpuAddition Normal RebootNode"},
	          {fts,"http://someserver.ericsson.se/test_doc4711.pdf"}]}                  
            ].</pre>

  </section>

  <section>
    <marker id="suite"></marker>
    <title>Test suite info function</title>

      <p>The <c>suite/0</c> function can be used in a test suite
	module to set the default values for the <c>timetrap</c> and
	<c>require</c> tags. If a test case info function also specifies
	any of these tags, the default value is overruled. See above for
	more information.
      </p>
      
      <p>Other options that may be specified with the suite info list are:</p>
      <list>
	<item><c>stylesheet</c>, 
	  see <seealso marker="run_test_chapter#html_stylesheet">HTML Style Sheets</seealso>.</item>
	<item><c>userdata</c>, 
	  see <seealso marker="#info_function">Test case info function</seealso>.</item>
	<item><c>silent_connections</c>, 
	  see <seealso marker="run_test_chapter#silent_connections">Silent Connections</seealso>.</item>
      </list>

       <p>
	Example of the suite info function:
      </p>
      <pre>
	suite() ->
	    [
	     {timetrap,{minutes,10}},
	     {require,global_names},
	     {userdata,[{info,"This suite tests database transactions."}]},
	     {silent_connections,[telnet]},
	     {stylesheet,"db_testing.css"}
            ].</pre>    
    
  </section>

  <section>
    <marker id="test_case_groups"></marker>
    <title>Test case groups</title>
    <p>A test case group is a set of test cases that share configuration 
    functions and execution properties. Test case groups are defined by
    means of the <c>groups/0</c> function according to the following syntax:</p>
    <pre>
      groups() -> GroupDefs

      Types:

      GroupDefs = [GroupDef]
      GroupDef = {GroupName,Properties,GroupsAndTestCases}
      GroupName = atom()
      GroupsAndTestCases = [GroupDef | {group,GroupName} | TestCase]
      TestCase = atom()</pre>

    <p><c>GroupName</c> is the name of the group and should be unique within
    the test suite module. Groups may be nested, and this is accomplished
    simply by including a group definition within the <c>GroupsAndTestCases</c>
    list of another group. <c>Properties</c> is the list of execution 
    properties for the group. The possible values are:</p>
    <pre>
      Properties = [parallel | sequence | Shuffle | {RepeatType,N}]
      Shuffle = shuffle | {shuffle,Seed}
      Seed = {integer(),integer(),integer()}
      RepeatType = repeat | repeat_until_all_ok | repeat_until_all_fail |
                   repeat_until_any_ok | repeat_until_any_fail
      N = integer() | forever</pre>

    <p>If the <c>parallel</c> property is specified, Common Test will execute
    all test cases in the group in parallel. If <c>sequence</c> is specified,
    the cases will be executed in a sequence, as described in the chapter
    <seealso marker="dependencies_chapter#sequences">Dependencies between 
    test cases and suites</seealso>. If <c>shuffle</c> is specified, the cases
    in the group will be executed in random order. The <c>repeat</c> property
    orders Common Test to repeat execution of the cases in the group a given
    number of times, or until any, or all, cases fail or succeed.</p>

    <p>Example:</p>
    <pre>
      groups() -> [{group1, [parallel], [test1a,test1b]},
                   {group2, [shuffle,sequence], [test2a,test2b,test2c]}].</pre>

    <p>To specify in which order groups should be executed (also with respect
    to test cases that are not part of any group), tuples on the form 
    <c>{group,GroupName}</c> should be added to the <c>all/0</c> list. Example:</p>
    <pre>
      all() -> [testcase1, {group,group1}, testcase2, {group,group2}].</pre>

    <p>Properties may be combined so that e.g. if <c>shuffle</c>, 
    <c>repeat_until_any_fail</c> and <c>sequence</c> are all specified, the test 
    cases in the group will be executed repeatedly and in random order until
    a test case fails, when execution is immediately stopped and the rest of 
    the cases skipped.</p>

    <p>Before execution of a group begins, the configuration function
    <c>init_per_group(GroupName, Config)</c> is called (the function is
    mandatory if one or more test case groups are defined). The list of tuples 
    returned from this function is passed to the test cases in the usual 
    manner by means of the <c>Config</c> argument. <c>init_per_group/2</c>
    is meant to be used for initializations common for the test cases in the
    group. After execution of the group is finished, the 
    <c>end_per_group(GroupName, Config</c> function is called. This function
    is meant to be used for cleaning up after <c>init_per_group/2</c>.</p>

    <note><p><c>init_per_testcase/2</c> and <c>end_per_testcase/2</c>
    are always called for each individual test case, no matter if the case 
    belongs to a group or not.</p></note>

    <p>The properties for a group is always printed on the top of the HTML log 
    for <c>init_per_group/2</c>. Also, the total execution time for a group
    can be found at the bottom of the log for <c>end_per_group/2</c>.</p>

    <p>Test case groups may be nested so that sets of groups can be 
    configured with the same <c>init_per_group/2</c> and <c>end_per_group/2</c>
    functions. Nested groups may be defined by including a group definition,
    or a group name reference, in the test case list of another group. Example:</p>
    <pre>
      groups() -> [{group1, [shuffle], [test1a,
                                        {group2, [], [test2a,test2b]},
                                        test1b]},
                   {group3, [], [{group,group4},
                                 {group,group5}]},
                   {group4, [parallel], [test4a,test4b]},
                   {group5, [sequence], [test5a,test5b,test5c]}].</pre>

    <p>In the example above, if <c>all/0</c> would return group name references
    in this order: <c>[{group,group1},{group,group3}]</c>, the order of the 
    configuration functions and test cases will be the following (note that
    <c>init_per_testcase/2</c> and <c>end_per_testcase/2:</c> are also
    always called, but not included in this example for simplification):</p>
    <pre>
-      init_per_group(group1, Config) -> Config1  (*)

--          test1a(Config1)

--	    init_per_group(group2, Config1) -> Config2

---              test2a(Config2), test2b(Config2)

--          end_per_group(group2, Config2)

--          test1b(Config1)

-      end_per_group(group1, Config1) 

-      init_per_group(group3, Config) -> Config3

--          init_per_group(group4, Config3) -> Config4

---              test4a(Config4), test4b(Config4)  (**)

--          end_per_group(group4, Config4)

--	    init_per_group(group5, Config3) -> Config5

---              test5a(Config5), test5b(Config5), test5c(Config5)

--          end_per_group(group5, Config5)

-      end_per_group(group3, Config3)


    (*) The order of test case test1a, test1b and group2 is not actually
        defined since group1 has a shuffle property.

    (**) These cases are not executed in order, but in parallel.</pre>

    <p>Properties are not inherited from top level groups to nested 
    sub-groups. E.g, in the example above, the test cases in <c>group2</c> 
    will not be executed in random order (which is the property of 
    <c>group1</c>).</p>
  </section>

  <section>
    <title>The parallel property and nested groups</title>
    <p>If a group has a parallel property, its test cases will be spawned
    simultaneously and get executed in parallel. A test case is not allowed
    to execute in parallel with <c>end_per_group/2</c> however, which means
    that the time it takes to execute a parallel group is equal to the
    execution time of the slowest test case in the group. A negative side
    effect of running test cases in parallel is that the HTML summary pages
    are not updated with links to the individual test case logs until the 
    <c>end_per_group/2</c> function for the group has finished.</p>

    <p>A group nested under a parallel group will start executing in parallel 
    with previous (parallel) test cases (no matter what properties the nested 
    group has). Since, however, test cases are never executed in parallel with 
    <c>init_per_group/2</c> or <c>end_per_group/2</c> of the same group, it's 
    only after a nested group has finished that any remaining parallel cases 
    in the previous group get spawned.</p>
  </section>

  <section>
    <title>Repeated groups</title>
    <marker id="repeated_groups"></marker>
    <p>A test case group may be repeated a certain number of times
    (specified by an integer) or indefinitely (specified by <c>forever</c>).
    The repetition may also be stopped prematurely if any or all cases
    fail or succeed, i.e. if the property <c>repeat_until_any_fail</c>,
    <c>repeat_until_any_ok</c>, <c>repeat_until_all_fail</c>, or 
    <c>repeat_until_all_ok</c> is used. If the basic <c>repeat</c>
    property is used, status of test cases is irrelevant for the repeat 
    operation.</p>
    
    <p>It is possible to return the status of a sub-group (ok or
    failed), to affect the execution of the group on the level above. 
    This is accomplished by, in <c>end_per_group/2</c>, looking up the value
    of <c>tc_group_properties</c> in the <c>Config</c> list and checking the
    result of the test cases in the group. If status <c>failed</c> should be
    returned from the group as a result, <c>end_per_group/2</c> should return
    the value <c>{return_group_result,failed}</c>. The status of a sub-group
    is taken into account by Common Test when evaluating if execution of a
    group should be repeated or not (unless the basic <c>repeat</c>
    property is used).</p>

    <p>The <c>tc_group_properties</c> value is a list of status tuples, 
    each with the key <c>ok</c>, <c>skipped</c> and <c>failed</c>. The
    value of a status tuple is a list containing names of test cases 
    that have been executed with the corresponding status as result.</p>

    <p>Here's an example of how to return the status from a group:</p>
    <pre>
      end_per_group(_Group, Config) ->
          Status = ?config(tc_group_result, Config),
          case proplists:get_value(failed, Status) of
              [] ->                                   % no failed cases 
	          {return_group_result,ok};
	      _Failed ->                              % one or more failed
	          {return_group_result,failed}
          end.</pre>

    <p>It is also possible in <c>end_per_group/2</c> to check the status of
    a sub-group (maybe to determine what status the current group should also
    return). This is as simple as illustrated in the example above, only the
    name of the group is stored in a tuple <c>{group_result,GroupName}</c>,
    which can be searched for in the status lists. Example:</p>
    <pre>
      end_per_group(group1, Config) ->
          Status = ?config(tc_group_result, Config),
          Failed = proplists:get_value(failed, Status),
          case lists:member({group_result,group2}, Failed) of
	        true ->
		    {return_group_result,failed};
                false ->                                                    
	            {return_group_result,ok}
          end; 
      ...</pre>

    <note><p>When a test case group is repeated, the configuration 
    functions, <c>init_per_group/2</c> and <c>end_per_group/2</c>, are 
    also always called with each repetition.</p></note>
  </section>

  <section>
    <title>Shuffled test case order</title>
    <p>The order that test cases in a group are executed, is under normal
    circumstances the same as the order specified in the test case list 
    in the group definition. With the <c>shuffle</c> property set, however,
    Common Test will instead execute the test cases in random order.</p>

    <p>The user may provide a seed value (a tuple of three integers) with
    the shuffle property: <c>{shuffle,Seed}</c>. This way, the same shuffling
    order can be created every time the group is executed. If no seed value
    is given, Common Test creates a "random" seed for the shuffling operation 
    (using the return value of <c>erlang:now()</c>). The seed value is always
    printed to the <c>init_per_group/2</c> log file so that it can be used to
    recreate the same execution order in a subsequent test run.</p>

    <note><p>If a shuffled test case group is repeated, the seed will not
    be reset in between turns.</p></note>

    <p>If a sub-group is specified in a group with a <c>shuffle</c> property,
    the execution order of this sub-group in relation to the test cases 
    (and other sub-groups) in the group, is also random. The order of the
    test cases in the sub-group is however not random (unless, of course, the 
    sub-group also has a <c>shuffle</c> property).</p>
  </section>

  <section>
    <marker id="data_priv_dir"></marker>
    <title>Data and Private Directories</title>

    <p>The data directory (<c>data_dir</c>) is the directory where the
      test module has its own files needed for the testing. The name
      of the <c>data_dir</c> is the the name of the test suite followed
      by <c>"_data"</c>. For example,
      <c>"some_path/foo_SUITE.beam"</c> has the data directory
      <c>"some_path/foo_SUITE_data/"</c>. Use this directory for portability,
      i.e. to avoid hardcoding directory names in your suite. Since the data
      directory is stored in the same directory as your test suite, you should
      be able to rely on its existence at runtime, even if the path to your
      test suite directory has changed between test suite implementation and
      execution.
    </p>

<!--
    <p>
      When using the Common Test framework <c>ct</c>, automatic
      compilation of code in the data directory can be obtained by
      placing a makefile source called Makefile.src in the data
      directory. Makefile.src will be converted to a valid makefile by
      <c>ct</c> when the test suite is run. See the reference manual for
      the <c>ct</c> module for details about the syntax of Makefile.src.
    </p>
-->
    <p>
      The <c>priv_dir</c> is the test suite's private directory. This
      directory should be used when a test case needs to write to
      files. The name of the private directory is generated by the test
      server, which also creates the directory.
    </p>
    
      <note><p>You should not depend on current working directory for
	  reading and writing data files since this is not portable. All 
	  scratch files are to be written in the <c>priv_dir</c> and all 
	  data files should be located in <c>data_dir</c>. Note also that 
	  the Common Test server sets current working directory to the test case
	  log directory at the start of every case.
    </p></note>

  </section>

  <section>
    <title>Execution environment</title>

    <p>Each test case is executed by a dedicated Erlang process. The
      process is spawned when the test case starts, and terminated when
      the test case is finished. The configuration functions 
      <c>init_per_testcase</c> and <c>end_per_testcase</c> execute on the 
      same process as the test case.
    </p>

    <p>The configuration functions <c>init_per_suite</c> and 
      <c>end_per_suite</c> execute, like test cases, on dedicated Erlang
      processes.
    </p>
  </section>

  <section>
    <title>Timetrap timeouts</title>
    <marker id="timetraps"></marker>
    <p>The default time limit for a test case is 30 minutes, unless a
      <c>timetrap</c> is specified either by the suite info function
      or a test case info function. The timetrap timeout value defined
      in <c>suite/0</c> is the value that will be used for each test case
      in the suite (as well as for the configuration functions
      <c>init_per_suite/1</c> and <c>end_per_suite</c>). A timetrap timeout
      value set with the test case info function will override the value set
      by <c>suite/0</c>, but only for that particular test case.</p>
    <p>It is also possible to set/reset a timetrap during test case (or
      configuration function) execution. This is done by calling
      <c>ct:timetrap/1</c>. This function will cancel the current timetrap
      and start a new one.</p>
    <p>Timetrap values can be extended with a multiplier value specified at
      startup with the <c>multiply_timetraps</c> option. It is also possible
      to let Test Server decide to scale up timetrap timeout values
      automatically, e.g. if tools such as cover or trace are running during
      the test. This feature is disabled by default and can be enabled with
      the <c>scale_timetraps</c> start option.</p>
    <p>If a test case needs to suspend itself for a time that also gets
      multipled by <c>multiply_timetraps</c>, and possibly scaled up if
      <c>scale_timetraps</c> is enabled, the function <c>ct:sleep/1</c>
      may be called.</p>
  </section>

  <section>
    <title>Illegal dependencies</title>

    <p>Even though it is highly efficient to write test suites with
      the Common Test framework, there will surely be mistakes made,
      mainly due to illegal dependencies. Noted below are some of the 
      more frequent mistakes from our own experience with running the 
      Erlang/OTP test suites.</p>

    <list>

	<item>Depending on current directory, and writing there:<br></br>
	    
	    <p>This is a common error in test suites. It is assumed that
	      the current directory is the same as what the author used as
	      current directory when the test case was developed. Many test
	      cases even try to write scratch files to this directory. Instead
	      <c>data_dir</c> and <c>priv_dir</c> should be used to locate 
	      data and for writing scratch files.
	    </p>
	</item>

	<item>Depending on the Clearcase (file version control system) 
	  paths and files:<br></br>
	    
	    <p>The test suites are stored in Clearcase but are not 
	      (necessarily) run within this environment. The directory 
	      structure may vary from test run to test run.
	    </p>
	</item>

	<item>Depending on execution order:<br></br>
	
	    <p>During development of test suites, no assumption should be made
	    (preferrably) about the execution order of the test cases or suites.
	    E.g. a test case should not assume that a server it depends on,
	    has already been started by a previous test case. There are
	    several reasons for this:
	    </p>
	    <p>Firstly, the user/operator may specify the order at will, and maybe
	      a different execution order is more relevant or efficient on 
	      some particular occasion. Secondly, if the user specifies a whole 
	      directory of test suites for his/her test, the order the suites are
	      executed will depend on how the files are listed by the operating
	      system, which varies between systems. Thirdly, if a user
	      wishes to run only a subset of a test suite, there is no way
	      one test case could successfully depend on another.
	    </p>
	</item>

	<item>Depending on Unix:<br></br>
	    
	    <p>Running unix commands through <c>os:cmd</c> are likely 
	    not to work on non-unix platforms.
	    </p>
	</item>

	<item>Nested test cases:<br></br>

	    <p>Invoking a test case from another not only tests the same
	      thing twice, but also makes it harder to follow what exactly
	      is being tested. Also, if the called test case fails for some
	      reason, so will the caller. This way one error gives cause to
	      several error reports, which is less than ideal.
	    </p>
	    <p>Functionality common for many test case functions may be implemented
	      in common help functions. If these functions are useful for test cases
	      across suites, put the help functions into common help modules.
	    </p>
	</item>
	
      <item>Failure to crash or exit when things go wrong:<br></br>
	    
	    <p>Making requests without checking that the return value
	      indicates success may be ok if the test case will fail at a
	      later stage, but it is never acceptable just to print an error
	      message (into the log file) and return successfully. Such test cases
	      do harm since they create a false sense of security when overviewing
	      the test results.
	    </p>
	</item>

      <item>Messing up for subsequent test cases:<br></br>
	
	    <p>Test cases should restore as much of the execution
	      environment as possible, so that the subsequent test cases will
	      not crash because of execution order of the test cases. 
	      The function <c>end_per_testcase</c> is suitable for this.
	    </p>
	</item>
    </list>
  </section>
</chapter>