State Transition Testing

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State Transition Testing is a comprehensive testing approach that evaluates the functionality of a system or component by analyzing its response to changes in input conditions or modifications to its current state. This method involves the examination of the system's behavior against a sequence of specified input conditions. The system's output or component may vary based on the current conditions or its previous history, including the series of events that have occurred since its initiation. The system's state can be effectively summarized by utilizing the concept of states.

The concept of State Transition Testing is rooted in the seminal work of Alan Turing, who in 1936 invented the notion of the "a-machine." This innovative idea inspired the development of State Transition Testing as a method of evaluating the functionality of a system or component.

Table of Contents

  1. State Transition Example
  2. State Transition Table
  3. State Transition Diagram
  4. State Transition Test Coverage
  5. Advantages of State Transition Testing
  6. Disadvantages of State Transition Testing
  7. Video Tutorial

State Transition Example

State Transition Testing is a widely adopted testing approach that is especially suitable for menu-driven applications and the embedded software industry. This technique is also effective in modeling business scenarios with specific states or testing screen navigation. There are two primary methods for representing State Transitions: State Transition Diagrams and State Transition Tables. To illustrate the concept, let's examine the ATM Withdrawal process using a State Transition Diagram and a State Transition Table.

State Transition Table

A State Transition Table provides a comprehensive view of all valid and potential invalid transitions between states, including the events and resulting actions for valid transitions. The states are listed on the left side, while the events are described along the top. Each cell in the table represents the system's state after the event has occurred. This method is also referred to as a State Table and is useful in identifying invalid transitions.

 Event 1 (Insert Card)Event 2 (Enter PIN)Event 3 (PIN OK)Event 3 (PIN Not OK)
S1: StartS2---
S2: Wait for PIN-S3--
S3: 1st Try--S6S4
S4: 2nd Try--S6S5
S5: 3rd Try--S6S7
S6: Access to Account----
S7: Eat CardS1---

In the context of a Card Insertion scenario, the following State Transition occurs:

  • Upon Card Insertion, the system transitions to State 2: "Wait for Pin."
  • Upon Pin Entry, the system transitions to State 3: "1st Try."
  • Upon correct Pin Entry during any try, the system transitions to State 6: "Access to Account."
  • Upon incorrect Pin Entry during the 1st try, the system transitions to State 4: "2nd Try."
  • Upon incorrect Pin Entry during the 2nd try, the system transitions to State 5: "3rd Try."
  • Upon incorrect Pin Entry during the 3rd try, the system transitions to State 7: "Eat Card," after which the system returns to the Start State.

State Transition Diagram

State Transition Testing

A state transition diagram illustrates the possible software states and how the software enters, exits, and transitions between states. It has four main components:

  • States: State the software might get, or it is the current stage we are in while operating it. For example, waiting for the pin, accessing an account, or eating the card.
  • Transition: A transition is initiated by an event.
  • Events: The event results in a transition. Here, Event1: Card inserted, Event 2: enter Pin, Event 3: Pin OK, Event 4: Pin not OK
  • Actions: The state change may result in the software taking action. For example: outputting an invalid pin message.

The states are shown in a circle in the state transition diagram, and arrows represent the transition. It is also called State Chart or Graph. It is useful in identifying valid transitions. State transition diagrams usually show only valid transitions and exclude invalid ones.

State Transition Test Coverage

State Transition Testing enables the design of tests to encompass a range of scenarios, including a typical sequence of states, comprehensive examination of all states, testing of every transition, specific sequences of transitions, and testing of invalid transitions. The coverage of this testing technique is commonly quantified by determining the ratio of the number of identified states or transitions tested to the total number of identified states or transitions in the test object. This ratio is typically expressed as a percentage, effectively measuring the testing coverage achieved.

Advantages of State Transition Testing

The benefits of State Transition Testing include the following:

  • Improved Understanding of System Behavior: This testing technique facilitates a deeper understanding of the system's behavior under test.
  • Effective Representation of System Behavior: State Transition Testing provides a clear and concise representation of the system's behavior through pictorial or tabular representations. This helps the tester to cover and comprehend the system's behavior thoroughly.
  • Comprehensive Coverage of Conditions: State Transition Testing ensures the thorough examination of all relevant conditions and scenarios, providing confidence in the accuracy and completeness of the test results.
  • Effective Testing of System Transitions: The State Transition Testing Technique is particularly useful in testing various system transitions, ensuring that all conditions are covered, and the results are properly captured.

Disadvantages of State Transition Testing

The limitations of State Transition Testing include the following:

  • Limited Applicability: The method only applies in certain situations, as the system's possible states must be clearly defined. This can become a challenge in large systems as the number of states increases exponentially.
  • Reliability: The reliability of State Transition Testing may be compromised in certain scenarios, such as when sequential input combinations are not tested or when other functionalities require exploration through techniques such as Exploratory testing. As a result, it is essential to consider the suitability of this technique in the specific context of the system under test."