Quality Assurance: Reviews and Walkthroughs

1
Quality Assurance Reviews and Walkthroughs

• Arun Lakhotia
• University of Southwestern Louisiana
• Po Box 44330
• Lafayette, LA 70504, USA
• arun_at_cacs.usl.edu

2
Reference

• Steve McConnell, Code Complete, Microsoft Press,
  1993.
• See Chapter 24 and parts of Chapter 23
• Keywords
• Quality attributes
• Faults, failures
• Review
• Walkthrough

3
Terminology

• Failure
• Externally observable incorrect behavior
• Fault (bug, defect)
• Internal cause of the external failure
• Fix
• Change the internals or environment to remove the
  failure

4
Software quality characteristics

• Correctness
• Usability
• Efficiency
• Reliability
• Integrity
• Adaptability
• Robustness
• Accuracy
• Maintainability
• Flexibility
• Portability
• Reusability

• Readability
• Testability
• Understandability

5
Quality trade-offs

• Correctness
• Functioning exactly to specifications
• Adaptability
• Used in an environment or application for which
  it is not designed
• Robustness
• Functioning in the presence of invalid inputs
• Increasing one may decrease the other

6
Quality improvement techniques

• Dynamic -- by executing
• Unit testing
• Functional testing
• Static -- without executing
• Inspection
• Code walkthroughs
• Extern audit
• Code reading
• Desk check
• Proof of correctness
• Organizational
• Written quality objectives
• Development process
• Explicit QA activity
• Change control process

7
Effectiveness of QA techniques

• Percent of total defects found in the life of a
  system by a technique
• QA step Mean
• Desk checking (Design) - 35
• Informal review - 40
• Formal inspection (Design) - 55
• Formal inspection (Code) - 60
• Prototyping - 65
• Desk-checking code - 40
• Unit testing - 25
• Function testing - 35
• Integration testing - 45
• Field testing - 50

8
Cost of finding defects

• In the beginning static techniques are more
  expensive
• Overtime static techniques are cheaper and find
  higher number of bugs
• Code reading found 80 more faults per hour

9
Effectiveness of QA techniques

• No single technique finds greater than 65 (mean)
  errors
• Unit testing - only 25
• Combination of techniques needed
• Combining any two techniques may increase the
  detection rate two fold
• Static and dynamic processes find different types
  of defects
• Dynamic techniques find about 60

10
Cost of fixing defects

• How defects are found and the cost of fixing
  them.
• Inspection
• Finding and fixing in one step
• 3 hours per defect
• Testing
• Find failure
• Find case of failure (bug) and fix
• Two steps
• 12 hours per defect

11
Static techniques

• Also called Reviews
• Formal Inspection
• Code walkthroughs
• Code reading

12
Formal inspection

• Formal
• Well defined procedure
• Well defined roles
• Well defined expectations
• Well defined output

13
Formal Inspection Roles

• Moderator
• Author
• Reviewers
• Scribe
• but not Management
• The roles of moderator, author, and reviewer
  should be played by different people.

14
Formal Inspection Process

• Planning
• Author gives material to moderator
• Moderator identifies reviewers, provides them
• Material
• Checklist
• Overiew Author gives overview
• Preparation
• Reviewer work independently and review material
• Prepare a list of problems
• Based on checklist
• Inspection meeting
• Go over the material at a reasonable pace
• Identify defects
• Do not fix
• Scribe takes notes
• Report Rework Followup

15
Code walkthroughs

• Author
• identifies possible reviewers
• Gives them material
• Reviewers
• Read the code to find defects
• Give feedback in a meeting
• Emphasize on defect detection, not removal

16
Code Reading

• Author
• gives code to code readers
• Readers
• read it independently
• prepare a list of problems identified
• Give the list to the developer
• in meeting
• or outside meeting