Slide 6.1

CHAPTER 6

TESTING

Slide 6.2

Overview

Quality issues Nonexecution-based testing Execution-based testing What should be tested? Testing versus correctness proofs Who should perform execution-based testing? When testing stops?

Slide 6.3

Testing

Testing is an integral component of software process and an activity that must be carried out throughout the life cycle

Two types of testing– Execution-based testing– Nonexecution-based testing

Slide 6.4

Testing (contd)

“V & V”– Verification

» Determine if the phase was completed correctly » Performed at the end of each phase

– Validation» Determine if the product as a whole satisfies its requirements» Performed just before the product is delivered to the client

In this book, testing simply denotes V & V

Slide 6.5

Software Quality

Quality implies “excellence” of some sort In S/W, we do not strive for “excellence” but merely

getting the software to function correctly is enough That is, does the software satisfy its specifications? Read Just In Case You Wanted to Know on page 138

Software Quality Assurance (SQA)– Ensures that the product is correct– Performs testing at the end of each phase as well as at the end of

the product development– Managerial independence is important

» Development group

» SQA group

Slide 6.6

Nonexecution-Based Testing

Underlying principles– One should not review his or her own work– Why not?

Nonexecution-based testing is usually referred to as review

There are two types of reviews1. Walkthroughs

2. Inspections

Slide 6.7

Walkthroughs

Should consist of 4-6 members For example, a specification walkthrough should include

– Specification team manager & member– Client representative– Member that will perform the next phase (design team member)– SQA team member (should chair the walkthrough)

The material to be reviewed should be distributed in advance to the participants

Each reviewer should study the material and prepare two lists: – items that the reviewer does not understand– items that the reviewer believes incorrect

Slide 6.8

Walkthroughs (contd)

Walkthrough process– Usually no more than 2 hours– Detect and record faults – DO NOT correct– Two ways of conducting walkthroughs

1. Participant driven» Participants present their lists of unclear and incorrect items» The author must respond to each query

2. Document driven– The author walks the participants through the document– The reviewers interrupt whenever unclear or incorrect items

are presented

– The document-driven approach is usually more thorough (i.e., finds more faults)

Slide 6.9

Inspections

More detailed than walkthrough and has five formal steps: overview, preparation, inspection, rework and follow-up

Inspection team should consist of 4 members For example, design inspection team includes

– Moderator (inspection team leader), designer, implementer, tester

Slide 6.10

Inspection Steps

1. Overview– An overview of the document to be reviewed is given by one of

the authors– At the end of the overview session, the document is distributed to

the participants

2. Preparation– Participants try to understand the document in detail, aided by

statistics of fault types– Participants prepare the lists of unclear/incorrect items as well

3. Inspection– An author walks through the document with the inspection team– Faults are detected and recorded – DO NOT correct here– Within one day, the moderator generates a written report

containing faults detected during inspection

Slide 6.11

Inspection Steps (contd)

4. Rework– The author resolves all faults and problems noted in the written

report

5. Follow-up– The rework is thoroughly checked– All fixes must be checked to ensure that no new faults have been

introduced

Slide 6.12

Statistics on Inspections

82% of all detected faults (IBM, 1976) 70% of all detected faults (IBM, 1978) 93% of all detected faults (IBM, 1986) 90% decrease in cost of detecting fault

(Switching system, 1986) 4 major faults, 14 minor faults per 2 hours (JPL,

1990). Savings of $25,000 per inspection Number of faults decreased exponentially by

phase (JPL, 1992)

Slide 6.13

Metrics for Inspections

Fault density (e.g., faults per KLOC) Fault detection rate (e.g., faults detected per hour) Fault detection efficiency (e.g., the number of

faults detected per person-hour)

Slide 6.14

Execution-Based Testing

Definitions– Fault is the IEEE Standard terminology for “bug”– Failure is the observed incorrect behavior of the

product as a consequence of the fault– Error is the mistake made by programmer

“Programming testing can be a very effective way to show the presence of bugs, but it is hopelessly inadequate for showing their absence [Dijkstra, 1972]

Slide 6.15

What is execution-based testing?

“Execution-based testing is a process of inferring certain behavioral properties of a product based, in part, on the results of executing the product in known environment with selected inputs.” [Goodenough, 1979]– Inference (i.e., deriving logical conclusion)– Known environment– Selected inputs

What must be tested? => Behavioral properties of the product must be tested– Utility, reliability, robustness, performance and

correctness

Slide 6.16

Utility

Utility is the extent to which a user’s needs are met when a correct product is used under conditions permitted by its specifications

That is, does it meet user’s needs?– Ease of use– Useful functions– Cost-effectiveness

Slide 6.17

Reliability

Reliability is a measure of the frequency and criticality of product failure– How often does the product fail? (Mean time

between failures, MTBF)– How long does it take to restore? (Mean time to

restore, MTTR)– But often more important is how long it takes to

repair the results of the failure?

Slide 6.18

Robustness

Robustness is a function of a number of factors such as– Range of operating conditions– Possibility of unacceptable results with valid input– Effect of invalid input

Slide 6.19

Performance

Extent to which space and time constraints are met

Real-time systems have hard time constraints

Slide 6.20

Correctness

A product is correct if it satisfies its specifications

But what if the specifications themselves are incorrect?

Slide 6.21

Correctness of specifications

Incorrect specification for a sort

Function trickSort which satisfies this specification:

Slide 6.22

Correctness of specifications (contd)

Incorrect specification for a sort:

Corrected specification for the sort:

Slide 6.23

Correctness Proofs

Alternative to execution-based testing Read Section 6.5 on your own

Slide 6.24

Who Performs Execution-Based Testing?

Testing is destructive– A successful test finds a fault

Solution– 1. The programmer does informal testing– 2. SQA does systematic, thorough testing– 3. The programmer debugs the module

All test cases must be– Planned beforehand, including expected output– Retained afterwards

Slide 6.25

When Testing Can Stop?

Only when the product has been irrevocably retired

Read Chapter 6