Test vs. inspection Part 1 Tor Stålhane. What we will cover Part 1 – Introduction – Inspection processes – Testing processes Part 2 – Tests and inspections.

Test vs. inspectionPart 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

Adam’s data - 1Mean Time to Problem Occurrence – years

Product 1.6 5 16 50 160 500 1600 5000

1 0.7 1.2 2.1 5.0 10.3 17.8 28.8 34.2

2 0.7 1.5 3.2 4.3 9.7 18.2 28.0 34.3

3 0.4 1.4 2.8 6.5 8.7 18.0 28.5 33.7

4 0.1 0.3 2.0 4.4 11.9 18.7 28.5 34.2

5 0.7 1.4 2.9 4.4 9.4 18.4 28.5 34.2

6 0.3 0.8 2.1 5.0 11.5 20.1 28.2 32.0

7 0.6 1.4 2.7 4.5 9.9 18.5 28.5 34.0

8 1.1 1.4 2.7 6.5 11.1 18.4 27.1 31.9

9 0.0 0.5 1.9 5.6 12.8 20.4 27.6 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 muchWe can generate tests automatically, but would never the less have to use large resources to check the result – the oracle problem

A limit resultThe following relation holds under a rather wide

set of conditions:

The initial number of defects – N0 – must be estimated e.g. based on experience from earlier projects as number of defects per KLOC.

tN

eMTTFt

0ˆ

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 ofcompetence

Man Machine

Understanding Good at handling variations inwritten material

Bad at handling variations inwritten material

Observe General observations,multifunctional

Specialized, good at observingquantitative data, bad atpattern recognition

Reasoning Inductive, slow, imprecise butgood at error correction

Deductive, fast, precise butbad error correction

Memory Innovative, several accessmechanisms

Copying, formal access

Informationhandling

Single channel, less than 10bits per second

Multi channel, severalMegabits per second

Consistency Unreliable, get tired, dependson learning

Consistent repetition of several

actions

Power Low level, maximum ca. 150watt

High level over long periodsof time

Speed Slow – seconds 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 testsComplex 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 inspectionThe 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 consPros:• 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

The informal inspection process

Individualchecking

Planning

Product document

Changerequests

Rules,checklists,procedures

Loggingmeeting

Informal inspections – pros and consPros:• 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 planningCons:• 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

Formal inspection process overview

Walk-through

Kick-off Individualchecking

Edit and follow-up

Planning

Process improvements

Product document

Changerequests

Rules,checklists,procedures

Loggingmeeting

Distribution of resources

Activity Range %Typicalvalue %

Planning 3 – 5 4

Kick-off 4 – 7 6

Individual checking 20 – 30 25

Logging 20 – 30 25

Editing 15 – 30 20

Process brainstorming 15 – 30 16

Leader overhead, follow up, entry,exit

3 – 5 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 changesThis 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 processUnit 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 code3.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 processA 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 tests3. 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 environmentCons:• Might force the system to handle input that it

was not designed for, thus creating an unfavorable impression.