COIT20258

Software Engineering

Week 6: Software Testing

Understanding testing methodologies, strategies, and best practices

Today's Topics

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 & 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 & validation (V&V) process

Two Testing Goals

Validation Testing

To demonstrate to the developer & 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 behavior is incorrect or not in conformance with its specification

A successful test is a test that makes the system perform incorrectly & so exposes a defect

An Input-Output Model of Program Testing

Input test data (Ie)

Inputs causing anomalous behaviour

→

System

→

Output test results (Oe)

Outputs which reveal the presence of defects

Validation & Verification (V&V)

Validation

"Are we building the right product?"

The software should do what the user really requires; related to validation testing

Verification

"Are we building the product right?"

The software should conform to its specification; related to defect testing

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 & marketing environment:

Software purpose: The level of confidence depends on how critical the software is to an organization
User expectations: Users may have low expectations of certain kinds of software
Marketing environment: Getting a product to market early may be more important than finding defects

Inspections & Testing

Software Inspections

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

May be supplemented by tool-based document & code analysis

Software Testing

Concerned with exercising & observing product behaviour (dynamic verification)

The system is executed with test data & its operational behaviour is observed

Software Inspection

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

Inspections & Testing

Inspections & testing are complementary
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

A Model of the Software Testing Process

Design test cases

Create test scenarios

Prepare test data

Set up test inputs

Run program with test data

Execute tests

Compare results to test cases

Analyze outputs

Generate test reports

Document findings

Stages of Testing

Development Testing - discover bugs & defects during development

Release Testing - separate team tests complete version before release

User Testing - users test system in their own environment

Development Testing

Development testing includes all testing activities carried out by the team developing the system:

Unit Testing

Individual program units or object classes are tested. Focus on testing functionality of objects or methods.

Component Testing

Several individual units are integrated to create composite components. Focus on testing component interfaces.

System Testing

Some or all components in a system are integrated. 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 & 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 & interrogating all object attributes
Exercising the object in all possible states

Challenge: Inheritance makes it more difficult to design object class tests as the information to be tested is not localized

The Weather Station Object Interface

WeatherStation

identifier
reportWeather()
reportStatus()
powerSave(instruments)
remoteControl(commands)
reconfigure(commands)
restart(instruments)
shutdown(instruments)

Weather Station Testing

Need to define test cases for reportWeather, calibrate, test, startup & shutdown
Using a state model, identify sequences of state transitions to be tested & 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 & checked without manual intervention
In automated unit testing, you make use of a test automation framework (such as JUnit) to write & run your program tests

Benefit: Automation enables continuous testing and reduces human error in test execution

Automated Test Components

Setup Part

Initialize the system with the test case, namely the inputs & expected outputs

Call Part

Call the object or method to be tested

Assertion Part

Compare the result of the call with the expected result. If assertion evaluates to true, test successful; if false, test failed

Choosing Unit Test Cases

The test cases should show that, when used as expected, the component works correctly. If there are defects, these should be revealed by test cases.

Normal Operation Tests

Should reflect normal operation of a program & should show that the component works as expected

Abnormal Input Tests

Should use abnormal inputs to check that these are properly processed & do not crash the component

Testing Strategies

Partition Testing

Identify groups of inputs that have common characteristics & should be processed in the same way

You should choose tests from within each of these groups

Guideline-based Testing

Use testing guidelines to choose test cases

These guidelines reflect previous experience of the kinds of errors that programmers often make

Partition Testing

Input data & 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

Possible Inputs

Input equivalence partitions

→

System

→

Possible Outputs

Output partitions

Correct outputs

Equivalence Partitions Examples

Input Values

Less than 10000: 9999

Between 10000 and 99999: 10000, 50000, 99999

More than 99999: 100000

Number of Input Values

Less than 4: 3

Between 4 and 10: 4, 7, 10

More than 10: 11

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 & 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
You access the functionality of these objects through the defined component interface
Testing composite components should 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

The objective is to detect faults due to interface errors or invalid assumptions about interfaces

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 sub-systems

Interface Errors

Interface misuse

A calling component calls another component & makes an error in its use of its interface e.g., parameters in the wrong order

Interface misunderstanding

A calling component embeds assumptions about the behaviour of the called component which are incorrect

Timing errors

The called & the calling component operate at different speeds & out-of-date information is accessed

Interface Testing Guidelines

Design tests so that parameters to a called procedure are at the extreme ends of their ranges
Always test pointer parameters with null pointers
Design tests which cause the component to fail
Use stress testing in message passing systems
In shared memory systems, vary the order in which components are activated

System Testing

System testing during development involves integrating components to create a version of the system & then testing the integrated system
The focus in system testing is testing the interactions between components
System testing checks that components are compatible, interact correctly & transfer the right data at the right time across their interfaces
System testing tests the emergent behavior of a system

Use-Case Testing

Use cases developed to identify system interactions can be used as a basis for system testing
Each use case usually involves several system components so testing the use case forces these interactions to occur
The sequence diagrams associated with the use case documents the components & interactions that are being tested

Testing Policies

Exhaustive system testing is impossible so testing policies which define the required system test coverage may be developed

Examples of testing policies:

All system functions that are accessed through menus should be tested
Combinations of functions (e.g., text formatting) that are accessed through the same menu must be tested
Where user input is provided, all functions must be tested with both correct & incorrect input

Test-Driven Development

Test-driven development (TDD) is an approach to program development in which you inter-leave testing & code development
Tests are written before code & "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 Process

Identify new functionality

Define what to build

Write test

Create automated test

Run test

Execute (should fail)

Implement functionality

Write code to pass test

Refactor

Improve code quality

TDD Process Activities

Start by identifying the increment of functionality that is required. This should normally be small & implementable in a few lines of code
Write a test for this functionality & 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 & re-run the test
Once all tests run successfully, you move on to implementing the next chunk of functionality

Benefits of TDD

Code Coverage

Every code segment that you write has at least one associated test so all code written has at least one test

Regression Testing

A regression test suite is developed incrementally as a program is developed

Simplified Debugging

When a test fails, it should be obvious where the problem lies. The newly written code needs to be checked & modified

System Documentation

The tests themselves are a form of documentation that describe what the code should be doing

Regression Testing

Regression testing is testing the system to check that changes have not "broken" previously working code
In a manual testing process, regression testing is expensive but, with automated testing, it is simple & straightforward
All tests are rerun every time a change is made to the program
Tests must run "successfully" before the change is committed

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 is usually a black-box testing process where tests are only derived from the system specification

Release Testing & System Testing

Release testing is a form of system testing

Key Difference 1

A separate team that has not been involved in the system development, should be responsible for release testing

Key Difference 2

System testing by the development team should focus on discovering bugs in the system (defect testing). The objective of release testing is to check that the system meets its requirements & is good enough for external use (validation testing)

Requirements-Based Testing

Requirements-based testing involves examining each requirement & developing a test or tests for it

Mentcare system requirements example:

If a patient is known to be allergic to any particular medication, then prescription of that medication shall result in a warning message being issued to the system user
If a prescriber chooses to ignore an allergy warning, they shall provide a reason why this has been ignored

Requirements Tests

Set up a patient record with no known allergies. Prescribe medication for allergies that are known to exist. Check that a warning message is not issued by the system
Set up a patient record with a known allergy. Prescribe the medication that the patient is allergic to, & check that the warning is issued by the system
Set up a patient record in which allergies to two or more drugs are recorded. Prescribe both of these drugs separately & check that the correct warning for each drug is issued
Prescribe two drugs that the patient is allergic to. Check that two warnings are correctly issued
Prescribe a drug that issues a warning & overrule that warning. Check that the system requires the user to provide information explaining why the warning was overruled

A Usage Scenario for the Mentcare System

George is a nurse who specializes in mental healthcare. One of his responsibilities is to visit patients at home to check that their treatment is effective & that they are not suffering from medication side effects.

On a day for home visits, George logs into the Mentcare system & uses it to print his schedule of home visits for that day, along with summary information about the patients to be visited. He requests that the records for these patients be downloaded to his laptop. He is prompted for his key phrase to encrypt the records on the laptop.

One of the patients that he visits is Jim, who is being treated with medication for depression. Jim feels that the medication is helping him but believes that it has the side effect of keeping him awake at night. George looks up Jim's record & is prompted for his key phrase to decrypt the record.

Features Tested by Scenario Tests

Authentication by logging on to the system
Downloading & uploading of specified patient records to a laptop
Home visit scheduling
Encryption & decryption of patient records on a mobile device
Record retrieval & modification
Links with the drugs database that maintains side-effect information
The system for call prompting

Performance Testing

Part of release testing may involve testing the emergent properties of a system, such as performance & reliability
Tests should reflect the profile of use of the system
Performance tests usually involve planning a series of tests where the load is steadily increased until the system performance becomes unacceptable
Stress testing is a form of performance testing where the system is deliberately overloaded to test its failure behavior

User Testing

User or customer testing is a stage in the testing process in which users or customers provide input & advice on system testing
User testing is essential, even when comprehensive system & 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 & robustness of a system. These cannot be replicated in a testing environment

Types of User Testing

Alpha Testing

Users of the software work with the development team to test the software at the developer's site

Beta Testing

A release of the software is made available to users to allow them to experiment & to raise problems that they discover with the system developers

Acceptance Testing

Customers test a system to decide whether or not it is ready to be accepted from the system developers & deployed in the customer environment. Primarily for custom systems

The Acceptance Testing Process

Define acceptance criteria

Establish standards

Plan acceptance testing

Create test strategy

Derive acceptance tests

Design specific tests

Run acceptance tests

Execute test cases

Negotiate test results

Review findings

Accept or reject system

Make final decision

Stages of the Acceptance Testing

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

Agile Methods & Acceptance Testing

In agile methods, the user/customer is part of the development team & is responsible for making decisions on the acceptability of the system
Tests are defined by the user/customer & 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' & can represent the interests of all system stakeholders

Key Points

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, component testing, and system testing

Key Points (Continued)

When testing software, you should try to 'break' the software by using experience & 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 & 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 & used in its operational environment

Summary

Today we covered:

The fundamentals of software testing and V&V
Development testing strategies (Unit, Component, System)
Test-driven development approach
Release testing and requirements validation
User testing methods including acceptance testing

Remember: Testing shows the presence of bugs, not their absence!

Questions & Discussion

Think about:

How would you apply TDD to your current projects?
What testing strategies are most relevant to your domain?
How can you balance testing thoroughness with development speed?
What role should users play in your testing process?

Next Week

We'll continue our exploration of software engineering by examining:

Software maintenance and evolution
Legacy system management
Software re-engineering
Configuration management

Preparation: Review today's testing concepts and think about how they apply to long-term software maintenance

Additional Resources

Testing Frameworks

JUnit (Java), pytest (Python), Jest (JavaScript), NUnit (.NET)

Books

"The Art of Software Testing" by Myers, Sandler & Badgett

Online Resources

Software Testing Help, Ministry of Testing community

Tools

Selenium (web testing), Postman (API testing), LoadRunner (performance)

Thank You

Questions?

COIT20258 - Software Engineering
Week 6: Software Testing