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

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<chapter>
  <header>
    <copyright>
      <year>2006</year><year>2013</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>Dependencies between Test Cases and Suites</title>
    <prepared>Peter Andersson</prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
    <file>dependencies_chapter.xml</file>
  </header>

  <section>
    <title>General</title>
    <p>When creating test suites, it is strongly recommended to not
      create dependencies between test cases, that is, letting test cases
      depend on the result of previous test cases. There are various
      reasons for this, such as, the following:</p>

    <list type="bulleted">
      <item>It makes it impossible to run test cases individually.</item>
      <item>It makes it impossible to run test cases in a different order.</item>
      <item>It makes debugging difficult (as a fault can be
	the result of a problem in a different test case than the one failing).</item>
      <item>There are no good and explicit ways to declare dependencies, so 
	it can be difficult to see and understand these in test suite 
	code and in test logs.</item>
      <item>Extending, restructuring, and maintaining test suites with 
	test case dependencies is difficult.</item>      
    </list>
    
    <p>There are often sufficient means to work around the need for test 
      case dependencies. Generally, the problem is related to the state of 
      the System Under Test (SUT). The action of one test case can change the 
      system state. For some other test case to run properly, this new state 
      must be known.</p>

    <p>Instead of passing data between test cases, it is recommended
      that the test cases read the state from the SUT and perform assertions
      (that is, let the test case run if the state is as expected, otherwise reset or fail).
      It is also recommended to use the state to set variables necessary for the 
      test case to execute properly. Common actions can often be implemented as 
      library functions for test cases to call to set the SUT in a required state. 
      (Such common actions can also be separately tested, if necessary,
      to ensure that they work as expected). It is sometimes also possible, 
      but not always desirable, to group tests together in one test case, that is,
      let a test case perform a "scenario" test (a test consisting of subtests).</p>

    <p>Consider, for example, a server application under test. The following 
      functionality is to be tested:</p>
    
    <list type="bulleted">
      <item>Starting the server</item>
      <item>Configuring the server</item>
      <item>Connecting a client to the server</item>
      <item>Disconnecting a client from the server</item>
      <item>Stopping the server</item>
    </list>

    <p>There are obvious dependencies between the listed functions. The server cannot 
      be configured if it has not first been started, a client connot be connectd until 
      the server is properly configured, and so on. If we want to have one test 
      case for each function, we might be tempted to try to always run the
      test cases in the stated order and carry possible data (identities, handles,
      and so on) between the cases and therefore introduce dependencies between them.</p>

      <p>To avoid this, we can consider starting and stopping the server for every test.
      We can thus implement the start and stop action as common functions to be 
      called from 
      <seealso marker="common_test#Module:init_per_testcase-2"><c>init_per_testcase</c></seealso> and 
      <seealso marker="common_test#Module:end_per_testcase-2"><c>end_per_testcase</c></seealso>. 
      (Remember to test the start and stop functionality separately.) 
      The configuration can also be implemented as a common function, maybe grouped 
      with the start function. Finally, the testing of connecting and disconnecting a 
      client can be grouped into one test case. The resulting suite can look as
      follows:</p>

    <pre>      
 -module(my_server_SUITE).
 -compile(export_all).
 -include_lib("ct.hrl").

 %%% init and end functions...

 suite() -> [{require,my_server_cfg}].

 init_per_testcase(start_and_stop, Config) ->
     Config;

 init_per_testcase(config, Config) ->
     [{server_pid,start_server()} | Config];

 init_per_testcase(_, Config) ->
     ServerPid = start_server(),
     configure_server(),
     [{server_pid,ServerPid} | Config].

 end_per_testcase(start_and_stop, _) ->
     ok;

 end_per_testcase(_, _) ->
     ServerPid = ?config(server_pid),
     stop_server(ServerPid).

 %%% test cases...

 all() -> [start_and_stop, config, connect_and_disconnect].

 %% test that starting and stopping works
 start_and_stop(_) ->
     ServerPid = start_server(),
     stop_server(ServerPid).

 %% configuration test
 config(Config) ->
     ServerPid = ?config(server_pid, Config),
     configure_server(ServerPid).

 %% test connecting and disconnecting client
 connect_and_disconnect(Config) ->
     ServerPid = ?config(server_pid, Config),
     {ok,SessionId} = my_server:connect(ServerPid),
     ok = my_server:disconnect(ServerPid, SessionId).

 %%% common functions...

 start_server() ->
     {ok,ServerPid} = my_server:start(),
     ServerPid.

 stop_server(ServerPid) ->
     ok = my_server:stop(),
     ok.

 configure_server(ServerPid) ->
     ServerCfgData = ct:get_config(my_server_cfg),
     ok = my_server:configure(ServerPid, ServerCfgData),
     ok.</pre>

    </section>

    <section>
    <marker id="save_config"></marker>
      <title>Saving Configuration Data</title>

      <p>Sometimes it is impossible, or infeasible, to
	implement independent test cases. Maybe it is not possible to read the 
	SUT state. Maybe resetting the SUT is impossible and it takes too long time
	to restart the system. In situations where test case dependency is necessary,
	CT offers a structured way to carry data from one test case to the next. The
	same mechanism can also be used to carry data from one test suite to the next.</p>

      <p>The mechanism for passing data is called <c>save_config</c>. The idea is that
	one test case (or suite) can save the current value of <c>Config</c>, or any list of
	key-value tuples, so that the next executing test case (or test suite) can read it. 
	The configuration data is not saved permanently but can only be passed from one 
        case (or suite) to the next.</p>

      <p>To save <c>Config</c> data, return tuple <c>{save_config,ConfigList}</c>
         from <c>end_per_testcase</c> or from the main test case function.</p>

      <p>To read data saved by a previous test case, use macro <c>config</c> with a 
	<c>saved_config</c> key as follows:</p>
      
      <p><c>{Saver,ConfigList} = ?config(saved_config, Config)</c></p>

      <p><c>Saver</c> (<c>atom()</c>) is the name of the previous test case (where the
	data was saved). The <c>config</c> macro can be used to extract particular data
	also from the recalled <c>ConfigList</c>. It is strongly recommended that 
	<c>Saver</c> is always matched to the expected name of the saving test case. 
	This way, problems because of restructuring of the test suite can be avoided. 
	Also, it makes the dependency more explicit and the test suite easier to read 
        and maintain.</p>

      <p>To pass data from one test suite to another, the same mechanism is used. The data
	is to be saved by finction
	<seealso marker="common_test#Module:end_per_suite-1"><c>end_per_suite</c></seealso> 
	and read by function
	<seealso marker="common_test#Module:init_per_suite-1"><c>init_per_suite</c></seealso>
	in the suite that follows. When passing data between suites, <c>Saver</c> carries the 
	name of the test suite.</p>

      <p><em>Example:</em></p>
      
      <pre>
 -module(server_b_SUITE).
 -compile(export_all).
 -include_lib("ct.hrl").

 %%% init and end functions...

 init_per_suite(Config) ->
     %% read config saved by previous test suite
     {server_a_SUITE,OldConfig} = ?config(saved_config, Config),
     %% extract server identity (comes from server_a_SUITE)
     ServerId = ?config(server_id, OldConfig),
     SessionId = connect_to_server(ServerId),
     [{ids,{ServerId,SessionId}} | Config].

 end_per_suite(Config) ->
     %% save config for server_c_SUITE (session_id and server_id)
     {save_config,Config}

 %%% test cases...

 all() -> [allocate, deallocate].

 allocate(Config) ->
     {ServerId,SessionId} = ?config(ids, Config),
     {ok,Handle} = allocate_resource(ServerId, SessionId),
     %% save handle for deallocation test
     NewConfig = [{handle,Handle}],
     {save_config,NewConfig}.

 deallocate(Config) ->
     {ServerId,SessionId} = ?config(ids, Config),
     {allocate,OldConfig} = ?config(saved_config, Config),
     Handle = ?config(handle, OldConfig),
     ok = deallocate_resource(ServerId, SessionId, Handle).</pre>

      <p>To save <c>Config</c> data from a test case that is to be
        skipped, return tuple 
      <c>{skip_and_save,Reason,ConfigList}</c>.</p>

      <p>The result is that the test case is skipped with <c>Reason</c> printed to
      the log file (as described earlier) and <c>ConfigList</c> is saved 
      for the next test case. <c>ConfigList</c> can be read using 
      <c>?config(saved_config, Config)</c>, as described earlier. <c>skip_and_save</c>
      can also be returned from <c>init_per_suite</c>. In this case, the saved data can
      be read by <c>init_per_suite</c> in the suite that follows.</p>
    </section>

    <section>
    <marker id="sequences"></marker>
      <title>Sequences</title>

      <p>Sometimes test cases depend on each other so that
	if one case fails, the following tests are not to be executed.
        Typically, if the <c>save_config</c> facility is used and a test 
	case that is expected to save data crashes, the following 
	case cannot run. <c>Common Test</c> offers a way to declare such dependencies, 
	called sequences.</p>

      <p>A sequence of test cases is defined as a test case group
        with a <c>sequence</c> property. Test case groups are defined
	through function <c>groups/0</c> in the test suite (for details, see section
	<seealso marker="write_test_chapter#test_case_groups">Test Case Groups</seealso>.</p>

      <p>For example, to ensure that if <c>allocate</c>
	in <c>server_b_SUITE</c> crashes, <c>deallocate</c> is skipped,
	the following sequence can be defined:</p>
      
      <pre>
 groups() -> [{alloc_and_dealloc, [sequence], [alloc,dealloc]}].</pre>

      <p>Assume that the suite contains the test case <c>get_resource_status</c> 
	that is independent of the other two cases, then function <c>all</c> can 
	look as follows:</p>

      <pre>
 all() -> [{group,alloc_and_dealloc}, get_resource_status].</pre>

      <p>If <c>alloc</c> succeeds, <c>dealloc</c> is also executed. If <c>alloc</c> fails
	however, <c>dealloc</c> is not executed but marked as <c>SKIPPED</c> in the HTML log. 
	<c>get_resource_status</c> runs no matter what happens to the <c>alloc_and_dealloc</c>
	cases.</p>

      <p>Test cases in a sequence are executed in order until all succeed or 
	one fails. If one fails, all following cases in the sequence are skipped.
	The cases in the sequence that have succeeded up to that point are reported as 
	successful in the log. Any number of sequences can be specified.</p>
	<p><em>Example:</em></p>

      <pre>
 groups() -> [{scenarioA, [sequence], [testA1, testA2]}, 
              {scenarioB, [sequence], [testB1, testB2, testB3]}].

 all() -> [test1, 
           test2, 
           {group,scenarioA}, 
	   test3, 
           {group,scenarioB}, 
           test4].</pre>

      <p>A sequence group can have subgroups. Such subgroups can have 
        any property, that is, they are not required to also be sequences. If you want the 
	status of the subgroup to affect the sequence on the level above, return 
	<c>{return_group_result,Status}</c> from 
	<seealso marker="common_test#Module:end_per_group-2"><c>end_per_group/2</c></seealso>, 
	as described in section
	<seealso marker="write_test_chapter#repeated_groups">Repeated Groups</seealso>
	in Writing Test Suites.
	A failed subgroup (<c>Status == failed</c>) causes the execution of a 
	sequence to fail in the	same way a test case does.</p>
    </section>
</chapter>