Software Testing

We have a few titles on this topic. Let’s list them.

• Development testing
• Test-driven development
• Release testing
• User testing

Program Testing

Testing is intended to show that a program does what it is intended to do and to discover program defects before it is put into use. When you test software, you execute a program using artificial data. You check the results of the test run for errors, anomalies or information about the program’s non-functional attributes. Can reveal the presence of errors NOT their absence. Testing is part of a more general verification and validation process, which also includes static validation techniques.

Program Testing Goals

To demonstrate to the developer and the customer that the software meets its requirements.
For custom software, this means that there should be at least one test for every requirement in the requirements document. For generic software products, it means that there should be tests for all of the system features, plus combinations of these features, that will be incorporated in the product release.

To discover situations in which the behavior of the software is incorrect, undesirable or does not conform to its specification.
Defect testing is concerned with rooting out undesirable system behavior such as system crashes, unwanted interactions with other systems, incorrect computations and data corruption.

Validation and defect testing

The first goal leads to validation testing
- You expect the system to perform correctly using a given set of test cases that reflect the system’s expected use.
The second goal leads to defect testing
- The test cases are designed to expose defects. The test cases in defect testing can be deliberately obscure and need not reflect how the system is normally used.

Testing process goals

Validation testing
- To demonstrate to the developer and the system customer that the software meets its requirements
- A successful test shows that the system operates as intended.
Defect testing
- To discover faults or defects in the software where its behaviour is incorrect or not in conformance with its specification
- A successful test is a test that makes the system perform incorrectly and so exposes a defect in the system.

Verification vs Validation

Verification: “Are we building the product right”. The software should conform to its specification.
Validation: “Are we building the right product”. The software should do what the user really requires.

V & V Confidence

Aim of V & V is to establish confidence that the system is ‘fit for purpose’.
Depends on system’s purpose, user expectations and marketing environment
1-Software purpose
- The level of confidence depends on how critical the software is to an organisation.
2- User expectations
- Users may have low expectations of certain kinds of software.
3- Marketing environment
- Getting a product to market early may be more important than finding defects in the program.

Inspections and Testing

Software inspections Concerned with analysis of the static system representation to discover problems (static verification)

Software testing Concerned with exercising and observing product behaviour (dynamic verification).

Software Inspections

These involve people examining the source representation with the aim of discovering anomalies and defects.
Inspections not require execution of a system so may be used before implementation.
They may be applied to any representation of the system (requirements, design,configuration data, test data, etc.).
They have been shown to be an effective technique for discovering program errors.

Advantages of Inspections

During testing, errors can mask (hide) other errors. Because inspection is a static process, you don’t have to be concerned with interactions between errors.
Incomplete versions of a system can be inspected without additional costs. If a program is incomplete, then you need to develop specialized test harnesses to test the parts that are available.
As well as searching for program defects, an inspection can also consider broader quality attributes of a program, such as compliance with standards, portability and maintainability.

Inspections and Testing

Inspections and testing are complementary and not opposing verification techniques.
Both should be used during the V & V process.
Inspections can check conformance with a specification but not conformance with the customer’s real requirements.
Inspections cannot check non-functional characteristics such as performance, usability, etc.

Stages of Testing

Development testing, where the system is tested during development to discover bugs and defects.
Release testing, where a separate testing team test a complete version of the system before it is released to users.
User testing, where users or potential users of a system test the system in their own environment.

<<<< Development testing >>>>>

Development testing includes all testing activities that are carried out by the team developing the system.
Unit testing, where individual program units or object classes are tested. Unit testing should focus on testing the functionality of objects or methods.
Component testing, where several individual units are integrated to create composite components. Component testing should focus on testing component interfaces.
System testing, where some or all of the components in a system are integrated and the system is tested as a whole. System testing should focus on testing component interactions.

Unit Testing

Unit testing is the process of testing individual components in isolation.
It is a defect testing process.
Units may be:
— Individual functions or methods within an object
— Object classes with several attributes and methods
— Composite components with defined interfaces used to access their functionality.

Object Class Testing

Complete test coverage of a class involves:
— Testing all operations associated with an object
— Setting and interrogating all object attributes
— Exercising the object in all possible states.
Inheritance makes it more difficult to design object class tests as the information to be tested is not localised.

Example : The weather station object interface

Need to define test cases for reportWeather, calibrate, test, startup and shutdown.
Using a state model, identify sequences of state transitions to be tested and the event sequences to cause these transitions
For example:
Shutdown -> Running-> Shutdown
Configuring-> Running-> Testing -> Transmitting -> Running
Running-> Collecting-> Running-> Summarizing -> Transmitting -> Running

Automated Testing

Whenever possible, unit testing should be automated so that tests are run and checked without manual intervention.
In automated unit testing, you make use of a test automation framework (such as JUnit) to write and run your program tests.
Unit testing frameworks provide generic test classes that you extend to create specific test cases. They can then run all of the tests that you have implemented and report, often through some GUI, on the success of otherwise of the tests.

Components :

A setup part, where you initialize the system with the test case, namely the inputs and expected outputs.
A call part, where you call the object or method to be tested.
An assertion part where you compare the result of the call with the expected result. If the assertion evaluates to true, the test has been successful if false, then it has failed.

Partition Testing

Input data and output results often fall into different classes where all members of a class are related.
Each of these classes is an equivalence partition or domain where the program behaves in an equivalent way for each class member.
Test cases should be chosen from each partition.

Equivalence partitioning

Equivalence partitions

Testing guidelines (sequences)

Test software with sequences which have only a single value.
Use sequences of different sizes in different tests.
Derive tests so that the first, middle and last elements of the sequence are accessed.
Test with sequences of zero length.

General Testing Guidelines

Choose inputs that force the system to generate all error messages
Design inputs that cause input buffers to overflow
Repeat the same input or series of inputs numerous times
Force invalid outputs to be generated
Force computation results to be too large or too small.

Component Testing

Software components are often composite components that are made up of several interacting objects. For example, in the weather station system, the reconfiguration component includes objects that deal with each aspect of the reconfiguration.
- You access the functionality of these objects through the defined component interface.
-Testing composite components should therefore focus on showing that the component interface behaves according to its specification.
You can assume that unit tests on the individual objects within the component have been completed.

Interface Testing

Objectives are to detect faults due to interface errors or invalid assumptions about interfaces.
Interface types
- Parameter interfaces Data passed from one method or procedure to another.
Shared memory interfaces Block of memory is shared between procedures or functions.
- Procedural interfaces Sub-system encapsulates a set of procedures to be called by other sub-systems.
- Message passing interfaces Sub-systems request services from other subsystems

<<<<<<<<<< Test-driven development >>>>>>>

Test-driven development (TDD) is an approach to program development in which you inter-leave testing and code development.
Tests are written before code and ‘passing’ the tests is the critical driver of development.
You develop code incrementally, along with a test for that increment. You don’t move on to the next increment until the code that you have developed passes its test.
TDD was introduced as part of agile methods such as Extreme Programming. However, it can also be used in plan-driven development processes.

TDD (Test-Driven Development Process Activities)

Start by identifying the increment of functionality that is required. This should normally be small and implementable in a few lines of code.
Write a test for this functionality and implement this as an automated test.
Run the test, along with all other tests that have been implemented. Initially, you have not implemented the functionality so the new test will fail.
Implement the functionality and re-run the test.
Once all tests run successfully, you move on to implementing the next chunk of functionality.

Benefits of test-driven development

Code coverage
Regression testing
Simplified debugging
System documentation

<<<<<<<<Release Testing>>>>>>

Release testing is the process of testing a particular release of a system that is intended for use outside of the development team.
The primary goal of the release testing process is to convince the supplier of the system that it is good enough for use.
Release testing, therefore, has to show that the system delivers its specified functionality, performance and dependability, and that it does not fail during normal use.
Release testing is usually a black-box testing process where tests are only derived from the system specification.

<<<<< User Testing >>>>

User or customer testing is a stage in the testing process in which users or customers provide input and advice on system testing.
User testing is essential, even when comprehensive system and release testing have been carried out.
The reason for this is that influences from the user’s working environment have a major effect on the reliability, performance, usability and robustness of a system. These cannot be replicated in a testing environment.

Types of user testing

Alpha testing
Beta testing
Acceptance testing

Stages in the acceptance testing process

Define acceptance criteria
Plan acceptance testing
Derive acceptance tests
Run acceptance tests
Negotiate test results
Reject/accept system

Agile methods and Acceptance Testing

In agile methods, the user/customer is part of the development team and is responsible for making decisions on the acceptability of the system.
Tests are defined by the user/customer and are integrated with other tests in that they are run automatically when changes are made.
There is no separate acceptance testing process.
Main problem here is whether or not the embedded user is ‘typical’ and can represent the interests of all system stakeholders.

Summary for those who say the article is too long

Testing can only show the presence of errors in a program. It cannot demonstrate that there are no remaining faults.
Development testing is the responsibility of the software development team. A separate team should be responsible for testing a system before it is released to customers.
Development testing includes unit testing, in which you test individual objects and methods component testing in which you test related groups of objects and system testing, in which you test partial or complete systems.
When testing software, you should try to ‘break’ the software by using experience and guidelines to choose types of test case that have been effective in discovering defects in other systems.
Wherever possible, you should write automated tests. The tests are embedded in a program that can be run every time a change is made to a system.
Test-first development is an approach to development where tests are written before the code to be tested.
Scenario testing involves inventing a typical usage scenario and using this to derive test cases.
Acceptance testing is a user testing process where the aim is to decide if the software is good enough to be deployed and used in its operational environment.

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