lec 6 software faul-proneness

Why is fixing faults more expensive later in development?

Cost increases dramatically over time (e.g. up to 1000x more post-release)

What are software faults?

Defects or errors in software that cause incorrect or unexpected behaviour

What are the causes of software faults?

Incorrect requirements; Deviations from requirements; Logical coding errors; Testing inadequacies

Why are requirements a major cause of faults?

They may be incorrect, incomplete, or missing

What are types of requirement faults?

Incorrect definitions; Incomplete definitions; Missing requirements

How can ambiguous requirements be avoided?

Use measurable terms; Define performance metrics; Include examples; Validate with stakeholders

What is a deviation from requirements?

When implementation does not match specified requirements

Why do developers deviate from requirements?

Time pressure; Reuse of old code; Unapproved enhancements; Over-engineering

What are types of logical errors in coding?

Arithmetic; Control; Resource; Interface errors

Arithmetic errors (example)

Division by zero

Control errors (example)

Infinite loops

Resource errors (example)

Buffer overflow; Security violations

Interface errors (example)

Incompatible subsystems or mismatched interfaces

What are testing inadequacies?

Failures or weaknesses in the testing process

What are examples of testing inadequacies?

Incomplete test plans; Poor coverage; Missing boundary testing

What is line coverage?

Percentage of code lines executed during testing

What is branch coverage?

Percentage of decision branches executed during testing

What is fault density?

Number of faults divided by size of software

What factors affect interpretation of fault density?

Tester skill; Time spent testing; Severity/type of faults

Does low fault density mean good quality?

No, it may be due to poor testing or missed defects

What is Linus’ Law?

Given enough reviewers, bugs are easier to find

What is a limitation of Linus’ Law?

Too many reviewers give diminishing returns

What is Gall’s Law?

Complex systems evolve from simple working systems, not built from scratch

What are antipatterns?

Common but poor solutions that indicate deeper design problems

What are types of antipatterns?

Copy-paste; Poltergeist; Blob class; Frankencode; Broken windows; Duct tape coding

Copy-paste antipattern

Duplicated code leading to maintenance issues and widespread bugs

Poltergeist antipattern

Short-lived classes with little responsibility

Blob class antipattern

One large class handling too many responsibilities (violates SRP)

What are symptoms of a blob class?

Many fields; Many methods; Low cohesion; High coupling

Frankencode antipattern

Code pieces not designed to work together but forced into one system

Broken windows antipattern

Small issues left unfixed lead to overall code decay

Duct tape coder

Focuses on quick fixes without concern for quality or maintainability

What are debugging principles?

Fix one thing at a time; Question assumptions; Check recent changes; Use debugger; Break problems down; Check boundaries; Take breaks; Explain to others; Pair debug; Seek help

What is rubber duck debugging?

Explaining code line-by-line to identify issues

What is wolf fence debugging?

Divide problem repeatedly to isolate the issue (binary search approach)