Test vs. inspection Part 1

Tor Stålhane

What we will cover

• • Part 1 – Introduction – Inspection processes – Testing processes Part 2 – Tests and inspections – some data – Inspection as a social process – two experiments and some conclusions

Introduction

Product 1 2 3 4 5 6 7 8 9 1.6

0.7

0.7

0.4

0.1

0.7

0.3

0.6

1.1

0.0

Adam’s data - 1

Mean Time to Problem Occurrence – years 5 16 50 160 500 1600 1.2

2.1

5.0

10.3

17.8

28.8

1.5

1.4

0.3

1.4

0.8

1.4

1.4

0.5

3.2

2.8

2.0

2.9

2.1

2.7

2.7

1.9

4.3

6.5

4.4

4.4

5.0

4.5

6.5

5.6

9.7

8.7

11.9

9.4

11.5

9.9

11.1

12.8

18.2

18.0

18.7

18.4

20.1

18.5

18.4

20.4

28.0

28.5

28.5

28.5

28.2

28.5

27.1

27.6

5000 34.2

34.3

33.7

34.2

34.2

32.0

34.0

31.9

31.2

Adams’ data – 2

• • The main information that you get from the table on the previous slide is that Some defects are important because they will happen quite often.

Most defects are not important since they will happen seldom.

How can we tell the difference?

Testing alone is not the solution

• • As can be seen from the next slide, testing is not an acceptable solution alone. It will Take too long time Cost too much We can generate tests automatically, but would never the less have to use large resources to check the result – the oracle problem

A limit result

The following relation holds under a rather wide set of conditions:

MTTF t



e N

ˆ 0

t

The initial number of defects – N 0 – must be estimated e.g. based on experience from earlier projects as number of defects per KLOC.

An example from telecom

Testing and inspection – the V model

Testing and inspection – 1

The important message here is that testing cannot always be done. In the first, important phases, we have nothing to execute and will thus always have to do some type of inspection. This might be considered one of the weaknesses of traditional software engineering over Agile development.

Testing and inspection – 2

In order to understand the main differences between testing and inspection, we should consider Fits’ list.

Based on this, we will give a short discussion of the relative merits of testing and inspection.

Area of competence Understanding Observe Reasoning Memory Information handling Consistency Power Speed Man Machine Good at handling variations in written material General observations, multifunctional Inductive, slow, imprecise but good at error correction Innovative, several access mechanisms Single channel, less than 10 bits per second Unreliable, get tired, depends on learning Low level, maximum ca. 150 watt Slow – seconds Bad at handling variations in written material Specialized, good at observing quantitative data, bad at pattern recognition Deductive, fast, precise but bad error correction Copying, formal access Multi channel, several Megabits per second Consistent repetition of several actions High level over long periods of time Fast

Man vs. machine – 1

• • • Good when we need the ability to Handle variation Be innovative and inductive Recognize and handle patterns • • Not so good when we need the ability to Do the same things over and over again in a consistent manner Handle large amount of data

Man vs. machine – 2

• • In order to do the best job possible we need processes where we let each part Do what they are best at: – Man is innovative – Machine handles large amounts of data Support the other with their specialties.

– Machine supports man by making large amounts of information available – Man support machine by providing it with innovative input

General considerations - documents

Architecture, system, sub-system and component design plus pseudo code. Here we can only use inspections. Man will use experience and knowledge to identify possible problems Machine can support by identifying information – e.g. find all occurrences of a string.

General considerations – code (1)

For executable code, we can use inspection, testing or a combination of both. The size and complexity – degree of dynamism – of the code will, to a large degree, decide our choice.

• • Other important factors are the degree of experience with The programming language The algorithms used

General considerations – code (2)

• • Simple code Start with inspection – all code Design and run tests • • • Complex code Start with inspection – focus on algorithm and logic Decide test completeness criteria – we cannot test everything Design and run tests

Inspection processes

Inspections – 1

• • • The term “inspection” is often used in a rather imprecise manner. We will look at three types of inspection: Walkthrough Informal inspection – also called informal review Formal inspection – also called formal review or just inspection The first two types are usually project internal while the last one is used as a final acceptance activity for a document.

Inspections – 2

• • For all types of inspections: The quality of the results depends on the experience and knowledge of the participants. “Garbage in – Garbage out” It might be a good idea to involve customer representatives.

The walkthrough process

Walkthrough is a simple process – mostly used for early decisions for an activity. The document owner: 1. Makes a rough sketch of the solution – architecture, algorithm etc. 2. Presents – explain – the sketch to whoever shows up. 3. Registers feedback – improvements.

Walkthrough – pros and cons

• • Pros: Easy and inexpensive. Needs no extra preparation.

Collect ideas at an early stage of development.

• • Cons: No commitment from the participants May collect many loose or irrelevant ideas

Product document

The informal inspection process

Planning Rules, checklists, procedures Individual checking Logging meeting Change requests

Informal inspections – pros and cons

• • • • Pros: Is simple and inexpensive to perform.

Can be used at all stages of development Usually has a good cost / benefit ratio Needs a minimum of planning • • Cons: No participant commitment No process improvement

The formal inspection process

The formal inspection process described below is – with small variations – the most commonly used. The version shown on the following slides stem from T. Gilb and D. Graham. We recommend this process as the final acceptance process for all important documents

Product document

Formal inspection process overview

Change requests Planning Rules, checklists, procedures Process improvements Walk through Kick-off Individual checking Logging meeting Edit and follow up

Distribution of resources

Activity Planning Kick-off Individual checking Logging Editing Process brainstorming Leader overhead, follow up, entry, exit Range % 3 4 20 15 3 – – – 20 – 15 – – – 5 7 30 30 30 30 5 Typical value % 4 6 25 25 20 16 4

Initiating the inspection process

• • • The inspection process starts with a “request for inspection” from the author to the QA responsible.

The QA responsible appoints an inspection leader.

First step is always to check that the document is fit for inspection.

Planning

• Important planning points are: Who should participate in the inspections – Who is interested?

– Who have time available for preparation and meetings?

– Who has the necessary knowledge concerning application, language, tools, methods?

Kick-off

• • • Important activities here are: Distribution of necessary documents: – Documents that shall be inspected – Requirements – Applicable standards and checklists Assignment of roles and jobs Setting targets for resources, deadlines etc.

Individual checking

• • This is the main activity of the inspection. Each participant read the document to look for Potential errors - inconsistencies with requirements or common application experience Lack of adherence to company standards or good workmanship

Logging meeting

• • • The logging meeting has three purposes: Log issues already discovered by inspection participants Discover new issues based on discussions and new information that arises during the logging meeting.

Identify possible improvement to the inspection or development process.

Improve the product - 1

• • • The author receives the log from the inspection meeting. All items - issues - in the log are categorised as one of the following: Errors in the author’s document.

Errors in someone else’s document.

Misunderstandings in the inspection team.

Improve the product - 2

• • • Errors in own document: Make appropriate corrections Errors in someone else’s documents: Inform the owner of this document.

Misunderstandings in the inspection team: Improve document to avoid further misunderstandings.

Checking the changes

• • • This is the responsibility of the inspection leader. He must assure that all issues raised in the log are disposed of in a satisfactory manner: The documents that have been inspected Related documents - including standards and checklists Suggested process improvements

Formal inspection – pros and cons

• • Pros: Can be used to formally accept documents Includes process improvement • • Cons: Is time consuming and expensive Needs extensive planning in order to succeed

Testing processes

Testing

• • • We will look at three types of testing: Unit testing – does the code behave as intended. Usually done by the developer Function verification testing – also called systems test. Does the component or system provide the required functionality?

System verification testing – also called acceptance test. Does the hardware and software work together to give the user the intended functionality?

The unit testing process

Unit testing is done by the developer one or more times during development. It is a rather informal process which mostly run as follows: 1. Implement (part of) a component.

2. Define one or more tests to activate the code 3. Check the results against expectations and current understanding of the component

Unit testing – pros and cons

• • Pros: Simple way to check that the code works.

Can be used together with coding in an iterative manner.

• • Cons: Will only test the developer’s understanding of the spec.

May need stubs or drivers in order to test

The system test process

A systems test has the following steps: 1. Based on the requirements, identify – Test for each requirement, including error handling – Initial state, expected result and final state 2. Identify dependencies between tests 3. Identify acceptance criteria for test suite 4. Run tests and check results against – – Acceptance criteria for each test Acceptance criteria for the test suite

Systems test – pros and cons

• Pros: Tests system’s behavior against customer requirements.

• Cons: It is a black box test. If we find an error, the systems test must be followed by extensive debugging

The acceptance test process

• • • The acceptance test usually has three activities – all involving the customer or his representatives: Rerun the systems test at the customer’s site.

Use the system to solve a set of real-world tasks.

Try to break the system – by stressing it or by feeding it large amounts of illegal input

Acceptance test – pros and cons

• • Pros: Creates confidence that the system will be useful for the customer Shows the system’s ability to operate in the customer’s environment • Cons: Might force the system to handle input that it was not designed for, thus creating an unfavorable impression.