Software Testing for State Machines

Many varieties of software testing have gained prominence as developers search for ways to improve quality and meet project deadlines – code review, unit testing, regression testing, beta testing, test-driven development, and more. Regardless of a project’s goals or the source code language employed, it’s well accepted that the earlier a defect is found, the easier, cheaper, and more rapidly it can be fixed. Code generation from UML state machine diagrams, a new feature introduced in Altova UModel 2011 Release 2, can be used to validate conceptual logic very early in project development. Real-world design in a state machine diagram An example included with UModel provides a simple and realistic state machine diagram with a small test application you can run to see for yourself how easily it can be to test the logic of a design. The state machine diagram in the AirCondition.ump project in the UModel 2011 examples folder describes the operation of a typical heating and air conditioning system. The system includes a power button shown on the left side in the transition from the Off state, a modeSelect function that selects heating or cooling, a speedSelect function for the fan, and a standby button that puts the system in the standby mode shown on the right. The example project folder includes all the code generated for the diagram by UModel in Java, C#, and Visual Basic. To try out the Java version, all we have to do is use the command javac STMTester.java to compile the code and java STMTester to run it. The tester application displays a simulated control panel with information windows about the heating and air conditioning unit. The operating buttons appear along the top, the current state is described in the first window, and output messages generated by changes in the system appear in the second window. As shown above, the system initializes in the Off state, the mode is set to heater, and the fan is off. Before you operate the system, you might want to resize the control panel and state machine diagram to follow the actions of the tester application in the diagram itself, as shown in the reduced size image below. Operating the state machine When we click the powerButton, the Current state window is updated and a detailed description of the operations that occurred are listed as Event 1 in the Debug output messages window. If it’s a hot day, we might want to change the mode to Cooling and increase the fan speed, which we can do by clicking the modeSelect and speedSelect buttons. The Current state window updates with each click, and Event 2 and Event 3 are added to the output messages window. Now we can see how the tester application lets us fully exercise the logic of our state machine diagram by clicking every possible sequence of button selections to see if they produce the expected results. For instance if we put the unit in Standby mode (Event 4 below), then press speedSelect, we see in the output messages for Event 5 that no state change occurs in the substate named RegionSpeed. Compare Event 5 to Event 3 in the output messages window as shown below. Now that the system is in Standby mode and we don’t need any heating or cooling, let’s save energy by pressing the Power button to turn it off. Wait a second – it looks like nothing happened. No transition took place in Event 6, and the Current state in the top window is still Standby! Looking back at the state machine diagram, we can see the only way out of Standby mode is to press the Standby button again. Is that really the behavior an average user would expect, that the Power button would not turn off the system from Standby mode? Just imagine how expensive this issue could be to fix if it was first identified much later in product development when the prototype was being tested by a regulatory agency! Here’s a challenge we’ll throw out on the table for our readers: how would you design another more direct route from the Standby state to the Off state? Testing your own state machines You can use the UModel state machine code generation example projects as templates to create test applications for your own designs. You will want to take advantage of the UModel feature that automatically creates operations in a class as you add operation names to transitions in your state machine. Also, the UModel Help system includes detailed information about code generation from state machine diagrams and also uses the AirCondition.ump project file as an example. Find out for yourself how you can improve project development by testing the logic of your own state machine diagrams with Altova UModel – download a free 30-day trial today!