Übungen zurQualitätssicherung von Software (SWQS)

Prof. Dr. Holger Schlingloff

Humboldt-Universität zu Berlinund

Fraunhofer FOKUS

14.5.2013: Modellbasierter Test – Beispiel SATM

Folie 2H. Schlingloff, Software-Qualitätssicherung

Example: Automated Teller Machine

• “Simplified Automated Teller Machine” SATM• One of those common money distributors

Screen display, numerical keypad, card reader, cash dispensing unit, (receipt printer)

• Specification mostly given by screenshots (“rapid prototyping”) implicit information, e.g. which bills

are available• State-transition system

not much calculation user interaction Client-server paradigm

Folie 3H. Schlingloff, Software-Qualitätssicherung

SATM Description

• Description: Initially, the ATM displays the welcome screen. When the customer inserts a valid card, it asks to input the PIN. Afterwards, the customer can choose to display the balance or to withdraw money. If money withdrawal is chosen, the customer can select the amount and packaging of the money. The ATM then asks the bank for acknowledgement of the transaction. If the operation is acknowledged, it is performed and the customer is asked whether to perform another transaction. If the PIN is incorrect, the transaction is aborted and after three failed trials the card is kept. If the PIN is correct, the customer does not need to input it again when making a new transaction.

Your task:• Entities and events?• Interfaces?• Regions, states and transitions?

Folie 4H. Schlingloff, Software-Qualitätssicherung

•Entities and events?

• Interfaces?

Folie 5H. Schlingloff, Software-Qualitätssicherung

Designing a State Machine for the ATM

•Consider the „major operating modes“ of the ATM (idle, ready, waiting-for-PIN, ...)

•Can they be structured?

•Consider which values the variables have in these modes

•A state is a mapping of variables to values

•State transitions occur by environment interactions(or, rarely, by internal actions)

•Design an (incomplete) LTS for (part of) the ATMNow!