# Yggdrasil Tutorial

This tutorial explains the off-line test-case generation feature of Uppaal. An explanation of Yggdrasil is available in the help menu within Uppaal. Go to `Help Menu -> Help ...` and browse to `UPPAAL Help -> GUI Reference -> Yggdrasil`.

For comments or questions please contact Petur Olsen at `petur@cs.aau.dk`.

The features are explained in terms of two example systems. An On/Off system and an Up/Down counter. The systems are modeled in abstract terms, but could, respectively, represent a lamp with on/off capabilities and a dimmer lamp, which can be turned up or down.

Both examples include a model, decorated with test-code, a correct implementation of the system, and a mutant with an implementation error. The system and mutant are implemented in Java so they should be platform independent. Execution scripts are included for Windows and Linux.

## On/Off system

Open the onoff.xml file in Uppaal.

The system contains two templates: System and User.

The system can be either `On` or `Off`, with channels `on` and `off` changing between them.

The user can non-deterministically press `on` or `off`.

There are some Yggdrasil specific details in this model. First, there are two global variables declared:

    int __reach__ = 0;
    int __single__ = 0;

These are required for Yggdrasil to use depth-first reachability and single step techniques for test-case generation. These variables must not be altered in the model.

Second, there are two blocks of comments in the `System declarations`. A multi-line comment starting with `PREFIX` or `POSTFIX` is treated as prefix or postfix code for each test case.

In this example each test case is a Java class with a main method, executing this Java class constitutes running the test case. Therefore the prefix and postfix code is wrapper code for this Java class.

    /* PREFIX
      package app;
      import app.App;

      class Test extends App {

      public static void main(String[] args) {

    */

    /* POSTFIX
      }
    }
    */

The test case class extends the `App` class we are testing. Each step in the test case will execute some methods on this class.

The system model is decorated with test code. Double clicking the edge labeled `on?` and selecting the `Test Code` tab reveals an area for entering test code. In this model the test code should be `set_on();`. This will execute the method `set_on()` on the application whenever this edge is taken in a test case. Similarly `set_off();` is added to the edge labeled `off?`.

For states test code can be entered in two areas, `Enter` and `Exit`. This test code is added to the test case when the trace reaches the state or leaves it, respectively.

To generate test cases go to the `Yggdrasil` tab.

Select which techniques for test case generation to use. The different techniques are explained in the Uppaal Help Menu. For now only select `Depth search` and a depth of 20.

Select the output folder for test cases. Make this point to the `onoff` folder in this tutorial.

Pressing `Generate` should generate a single trace. Each trace generated will have a line in the list similar to `Trace coverage: 4/4`. This shows that the trace covered four out of four edges.

By double clicking the trace and selecting the `Simulator` tab, the trace can be examined. Unsurprisingly the trace simply runs in circles with alternating on/off presses.

Pressing the `Output` button in the `Yggdrasil` tab will generate a file called `testcase0.code` in the selected output folder. If several traces have been generated, several files will be generated with sequential numbering.

Each of these will be a Java class with the sequence of method invocations induce by the generated trace. A snippet is shown below.

     1: package app;
     2: import app.App;
     3:
     4: class Test extends App {
     5:
     6:     public static void main(String[] args) {
     7:
     8: expect_off();
     9:
    10: set_on();
    11:
    12: expect_on();
    13:
    14: set_off();
    15:
       <... snip ... >
    93:
    94:     }
    95: }

The test case starts with the prefix code on lines 1-6.

Line 8 is the first step of the trace. This is `expect_off();` since the initial location is `Off`.

The first transition is the one labeled `on?`, the test code for this transition is `set_on();`. This is entered in the trace at line 10.

The trace then enters location `On` and `expect_on();` is in the test case at line 12. The test case continues in this fashion.

The trace ends with the postfix code on lines 94-95.

Running the `test.sh` (or `test.bat` on Windows) will compile and run the test cases one at a time. It will output the name of each file as it executes them. No output from the test case signifies successful execution.

    onoff$ ./test.sh
    testcase0.code
    onoff$

Running the `testiMutant.sh` (or `testMutant.bat` on Windows) will compile and run the test cases on the mutant implementation. This should result in an exception being thrown, signifying a test error.

    onoff$ ./testMutant.sh
    testcase0.code
    Exception in thread "main" java.lang.AssertionError
      at app.App.expect_on(App.java:17)
      at app.Test.main(Test.java:15)
    onoff$

The implementation can be examined in the `onoff/app` folder. See AppC.java for the correct implementation and AppM.java for the mutant.

In order to transfer this to you own applications, you will have to decorate the model with test code such that the output from Yggdrasil constitutes an executable test case in whatever test execution framework you use.

Continue to part two of this tutorial for explanation of how values of parameters can be used in test cases.

Part two