Camunda Platform Scenario

This community extension to Camunda Platform enables you to write robust test suites for process models. The larger your process models, the more often you change them, the more value you will get out of using it. Look at a piece of test code:

@Test
public void testHappyPath() {
  // "given" part of the test
  when(process.waitsAtUserTask("CompleteWork")).thenReturn( 
    (task) -> task.complete()
  );
  // "when" part of the test
  run(process).startByKey("ReadmeProcess").execute();      
  // "then" part of the test  
  verify(process).hasFinished("WorkFinished");             
}

The code follows the GivenWhenThen style of representing tests.

The given part describes pre-conditions to the test: you define here a process scenario by coding actions to happen when the process arrives at waitstates such as user tasks, receive tasks, event based gateways etc.
The when part executes the specified scenario: it is now run through to its end
The then part describes the expected end state: you e.g. verify that the process instance reached an end event

Now look at the process under test. Aside of the "happy path", we also want to check the requirement that the colleague in charge of the work needs to be reminded daily to actually do it! 😄 In order to test time-related behaviour of processes, the library allows to "defer" actions for specified time periods. The following test code snippet verifies the example case, that the colleague should be reminded twice, in case he needs 2 1/2 days to complete the work.

@Test
public void testSlowPath() {
  when(process.waitsAtUserTask("CompleteWork")).thenReturn(
    (task) -> task.defer("P2DT12H", () -> task.complete())
  );
  when(process.waitsAtUserTask("RemindColleague")).thenReturn(
    (task) -> task.complete()
  );
  run(process).startByKey("ReadmeProcess").execute();
  verify(process).hasFinished("WorkFinished");
  verify(process, times(2)).hasFinished("ColleagueReminded");
}

Note that such time-aware scenarios work across interacting process instances and whole trees of call activities.

Our motivations

Camunda Platform Scenario enables much faster process development, removing the need to adapt unit test suites for large executable models over and over again. When using it we experience that just those tests need to break that we want to break: when we change the "business relevant" aspect under test or what the process achieves. However, our test suites do not break at all when we just refactor a model's inner logic or how we achieve the desired business semantics.

Furthermore, Camunda Platform Scenario enables realistic unit testing with respect to time-related process behaviour: by deferring actions and "fast-forwarding" test scenarios into their "process future", we can check how several processes and call activities behave together. We however always remain in the driver's seat: Camunda Platform Scenario works in a single-treaded, easily mockable and controllable unit test environment.

Show me more code!

The library provides you with a callback interface ProcessScenario. Implementing this interface allows you to define up front what needs to happen at the "waitstates" of your process under test. Typical "waitstates" are user tasks, receive tasks, intermediate catching events and some more, since Camunda Platform 7.4 in particular also "external" service tasks. But instead of simply implementing this interface you will typically mock its behaviour by making use of your preferred mocking framework. Let's look at an example using the Mockito framework:

@Mock private ProcessScenario insuranceApplication;
...
@Before
public void defineHappyScenario() {
  when(insuranceApplication.waitsAtUserTask("UserTaskDecideAboutApplication")).thenReturn((task) ->
    taskService.complete(task.getId(), Variables.putValue("approved", true))
  );
}

Note that there is no dependency to any mocking framework. The presented code snippet just happens to use Mockito to define that in case the ProcessScenario insuranceApplication arrives at and waits at the user task UserTaskDecideAboutApplication, we simply want to complete that task by passing a process variable approved = true. Once you have defined behaviour for all your process' waitstates you can execute such a scenario. There are several possibilities, the simplest of which would be to write:

@Test
public void testHappyPath() {
  Scenario.run(insuranceApplication).startByKey("InsuranceApplication").execute();
  ...
}

This means you start a new process instance by key and run it through to to its end. At the waitstates, your predefined actions apply, right? But obviously you also want to verify now "after the fact", that your process actually did what you really care about from a business perspective. It's worthwile to think about that notion a bit. We specified above that we approve the insurance application, so one thing we definitely care about is that our process reaches the "happy" end event. The full test case description could therefore look like:

@Test
public void testHappyPath() {
  // WHEN we execute the scenario with the default, "happy" waitstate behaviour ...
  Scenario.run(insuranceApplication).startByKey("InsuranceApplication").execute();
  // THEN we expect the process instance to finish with a "happy" end, the application being accepted ...
  verify(insuranceApplication).hasFinished("EndEventApplicationAccepted");
}

Note that in the last line, we simply consult the mocking framework to tell us about the interactions of our scenario execution with the ProcessScenario interface provided by us.

An extensive example: applying for insurance with "Camundanzia"! 😄

The following process scenario has been executed by means of Camunda Platform Scenario and has been visualised with the Camunda Process Test Coverage library:

Note that we see here a call activity Document Request invoked by an event sub process. Why does our scenario run show this path? Who takes care of the call activity's details? And why does the boundary timer 2 days actually trigger? Please have a look at the few lines of test code necessary to create this particular scenario!

Highlights

Define default waitstate actions once and override them with a different behaviour in your test methods
Eliminate almost all querying for runtime objects as e.g. tasks, you get the instances injected into your actions
Introduce or remove transaction borders ("savepoints": asyncBefore/asyncAfter) without affecting your tests
Execute several process instances alongside each other including whole trees of call activities
Enable realistic time-related unit testing by deferring waitstate actions for a period of time
Create a realistic history by defining time needed for all actions and "fast-forwarding" into the future
Use scenarios with the classic Camunda Platform Assert to verify current runtime state inside your waitstate actions

Just start to use it! Or are you too busy?

Camunda Platform Scenario is used in real life projects since years and works with all versions of Camunda Platform since 7.0 up to the most recent and all the Java versions (8, 11) relevant for Camunda Platform installations out there. This is continuously verified by executing more than 200 test cases against a travis ci test matrix.

^{Credits to https://hakanforss.wordpress.com}

Get started in 3 simple steps!

1. Add a maven test dependency to the last stable 1.x release or the upcoming 2.x release to your project:

Stable version 1.x

<dependency>
    <groupId>org.camunda.bpm.extension</groupId>
    <artifactId>camunda-bpm-assert-scenario</artifactId>
    <version>1.1.1</version>
    <scope>test</scope>
</dependency>

or upcoming version 2.x:

<dependency>
    <groupId>org.camunda.bpm.extension.scenario</groupId>
    <artifactId>camunda-platform-scenario-runner</artifactId>
    <version><!-- See version badge above -->></version>
    <scope>test</scope>
</dependency>

2. Add a mocked ProcessScenario to your test class

Create your test case just as described in the Camunda Platform Testing Guide. Then add Camunda Platform Scenario Runner by mocking its main interface - the example shown here makes use of Mockito:

ProcessScenario insuranceApplication = mock(ProcessScenario.class);
...
@Before
public void defineHappyScenario() {
  when(insuranceApplication.waitsAtUserTask("UserTaskDecideAboutApplication")).thenReturn((task) ->
    task.complete()
  );
}

3. Start executing and verifying your scenarios in your test methods

@Test
public void testHappyPath() {
  Scenario.run(insuranceApplication).startByKey("InsuranceApplication").execute();
  verify(insuranceApplication, times(1)).hasFinished("EndEventApplicationAccepted");
}

Green bar?

Congrats! You are successfully using Camunda Platform Scenario.

Add extensive logging to your tests

Turn on the logger 'org.camunda.bpm.scenario' and you will see detailed information about the execution of scenarios. The details of configuration depend on your logging framework - when using logback, you would e.g. write in logback.xml

<logger name="org.camunda.bpm.scenario" level="debug" /> <!-- or info -->

For optimally readably output, it can make a lot of sense to turn off all other logging, because scenario logging displays the "fast forwarding" of process time like e.g. shown in the following example test ouput:

...
| Started   receiveTask        'Wait for documents' (ReceiveTaskWaitForDocuments @ DocumentRequest # dad1fecf-dda0-11e6-906e-7ebec62e68c4)
* Acting on receiveTask        'Wait for documents' (ReceiveTaskWaitForDocuments @ DocumentRequest # dad1fecf-dda0-11e6-906e-7ebec62e68c4)
| Deferring action on          'Wait for documents' until 2017-01-25 18:10:21 (ReceiveTaskWaitForDocuments @ DocumentRequest # dad1fecf-dda0-11e6-906e-7ebec62e68c4 ...
| Fast-forwarding scenario to 2017-01-19 18:09:21
|-- Executing timer-transition   (BoundaryEventDaily @ DocumentRequest # dad1fecf-dda0-11e6-906e-7ebec62e68c4)
  | Started   boundaryTimer      'daily' (BoundaryEventDaily @ DocumentRequest # dad1fecf-dda0-11e6-906e-7ebec62e68c4)
  | Completed boundaryTimer      'daily' (BoundaryEventDaily @ DocumentRequest # dad1fecf-dda0-11e6-906e-7ebec62e68c4)
  | Started   sendTask           'Send reminder' (SendTaskSendReminder @ DocumentRequest # dad1fecf-dda0-11e6-906e-7ebec62e68c4)
  * Acting on sendTask           'Send reminder' (SendTaskSendReminder @ DocumentRequest # dad1fecf-dda0-11e6-906e-7ebec62e68c4)
  | Completed sendTask           'Send reminder' (SendTaskSendReminder @ DocumentRequest # dad1fecf-dda0-11e6-906e-7ebec62e68c4)
  | Started   noneEndEvent       'Reminder sent' (EndEvent_1 @ DocumentRequest # dad1fecf-dda0-11e6-906e-7ebec62e68c4)
  | Completed noneEndEvent       'Reminder sent' (EndEvent_1 @ DocumentRequest # dad1fecf-dda0-11e6-906e-7ebec62e68c4)
  | Fast-forwarding scenario to 2017-01-20 18:09:21
  |-- Executing timer-transition   (BoundaryEvent_2 @ InsuranceApplication # dacca880-dda0-11e6-906e-7ebec62e68c4)
    | Started   boundaryTimer      '2 days' (BoundaryEvent_2 @ InsuranceApplication # dacca880-dda0-11e6-906e-7ebec62e68c4)
    | Completed boundaryTimer      '2 days' (BoundaryEvent_2 @ InsuranceApplication # dacca880-dda0-11e6-906e-7ebec62e68c4)
    | Started   userTask           'Speed up manual check' (UserTaskSpeedUpManualCheck @ InsuranceApplication # dacca880-dda0-11e6-906e-7ebec62e68c4)
...

Whenever the scenario fast-forwards in time, the log output moves a bit to the right.

Further Resources

Maintenance & License

Martin Schimak
Company • GitHub • eMail
Apache License, Version 2.0

Contributions and Sponsorship

This library is written by Martin Schimak (plexiti) and evolved out of real life project needs at WDW eLab and in close collaboration with the software development team at WDW eLab's Vienna office. It could not have been brought to light without the open mindedness and open source mindedness I experienced with WDW eLab. You rock! 😄

You want to contribute? You are very welcome! Please contact me directly via eMail.

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