1 testing fundamentals

Fundamentals of Testing
 Why is testing necessary?
 What is testing?
 Testing Principles.
 Fundamental Test Process.
 How much testing is enough?
 Why Testers?

Why is testing necessary ?
 Software Systems Context
 Causes of Software Defects.
 Why we Test?
 Cost of Software Quality

 Software system context
 Software can be found in many areas of life.
 When a system go wrong, it can result many effects start
from user inconvenience ,including loss of money, time
or business reputation, and could even cause loss a life.

.
 Health equipment.
 Transportations.
 Banking
 Insurance
 Education
 Scientific Research

Errors
&
Mistakes
- Documents.
- Code
- Software system
Defect or Fault
Failure

 Causes of Software Defects
 Humans do mistakes.
 Mistakes may lead to defects in source code or system
specifications.
 Defects are detected only when they leads to failures
(code is executed), not all defects do so.
 Failures are considered problems when they occurred in
live systems.
 An observed failure is an incident.

Defect
Injection
Detection
Prevention
- A defect injected at the
time the causing error is
made.
- A defect is detected at
The time when failure
occurs.
- Finding defects in
requirements docs or static
code can prevent detecting
them in running systems.

Why is testing necessary?
 Why we Test (Testing Goals)
Find defects.
Measure quality.
Provide confidence.

Why is testing necessary?
 Costs of Software defects
 Msnbc published the news of 2010 bug hits millions of
German bank cards.
 Guardin.co.uk said they paid about (€300m).
 Apple Maps gives us directions to nowhere (2012).

Risks
(Poor
Quality)
Humans
(Death, Injury)
Economy
(Money, Time)
Business
(Revenue,
Reputation)

What is testing?
 The process consisting of all life cycle activities, both
static and dynamic concerned with planning ,
preparation and evaluation of software products and
related work products to determine that they satisfy
specified requirements , to demonstrate that they are
fit for purpose and to detect defects.

What is Testing?
 Executing SW is only part of testing ,other activities
exist before and after execution.
 Testing activities include: planning and control
,choosing test conditions , designing test cases and
checking results , evaluating exit criteria , reporting
and closure.

Suppose You are given “Pen” with instructions to test it .
What will you do ?

Testing
Static
Reviews
Dynamic
Functional
Non-
Functional
Performance
Security
Usability

 Testing Principles

Testing Principles
 Testing Shows Presence of defects.
 Exhaustive testing is impossible.
 Early Testing.
 Defect Clustering.
 Pesticide Paradox .
 Testing is context dependent.
 Absence of errors fallacy.

Testing Principles
 Testing Shows the presence of defects
 Testing can show that defects are present, but cannot
prove that there are no defects.
 Testing reduces the probability of undiscovered defects
remaining in the software.
 Discovering no more defects is not a proof of
correctness.

Testing principles
 Exhaustive testing is impossible
 Testing everything (all combinations of inputs and
preconditions) is not feasible except for trivial cases.
 Instead of exhaustive testing, risk analysis and priorities
should be used to focus testing efforts.
 Example: a simple screen with five input fields and 10
distinct values for each field has 10^5 different
combination.

Testing Principles
 Early Testing
 The earlier defects are detected , the lower the cost of
correction.
 To find defects early, testing activities shall be started as
early as possible in the software or system development
life cycle, and shall be focused on defined objectives.

Testing Principles
 Defect Clustering
 System modules vary in size, complexity and frequency
of change.
 System modules do not experience the same defect
density or failure rate.
 Thus, pareto principle (80-20 rule) is applicable:
A small number of modules contains most of the defects discovered
during prerelease testing , or show the most optional failures

Testing Principles
 Defect Clustering Cont’d
 When a defect is found in one area , changes are there
that more defects can be found and more time can be
invested there.
 Testers should not ignore any area as defects can be
scattered around

Testing Principles
 Pesticide Paradox
 If the same tests are repeated over and over again,
eventually the same set of test cases will no longer find
any new defects.
 To overcome this, test cases need to be regularly
reviewed and revised
 New and different tests need to be written to exercise
different parts of the software or system to find
potentially more defects.

Testing Principles
 Testing is context dependent
 Testing is done differently in different contexts.
 For example, safety-critical software is tested differently
from an e-commerce site.

Testing Principles
 Absence of Error Fallacy
 Finding and fixing defects does not help if the system
built is unusable and does not fulfill the users’ needs
and expectations.

 Fundamental Test Process

Planning
and
Control
Analysis
and
design
Implementation
and execution
Evaluating
Exit criteria
And
reporting
Closure

Fundamental Test Process
 Planning and Control
 Ongoing comparison of actual progress against plan.
 Reporting status.
 Takes into account feedback of monitoring and control.

 Analysis and Design
 Reviewing the test basis.
 Evaluating testability of test basis and test objects.
 Identifying and prioritizing test conditions
 Designing and prioritizing test cases.
 Identifying necessary test data.
 Designing the test environment set-up and identifying
any required infrastructure and tools.

 Implementation and execution
 Creating test cases , writing test procedures.
 Creating test suits.
 Prepare test execution plans.

 Evaluating Exit Criteria and Reporting
 Checking test logs against the exit criteria specified in
the planning.
 Assessing if more tests are needed.
 Writing a test summary report for stake holders.

 Test Closure
 Checking that deliverables have been delivered as
planned.
 Archiving the test environment and the test
infrastructure for later reuse.
 Analyzing lessons learned for future releases and
projects .

 How much testing is enough?

How much testing is enough?
 The amount of testing needed is proportionate with:
 Risk.
 Defect Cost.
 Information needed.
 Project constraints.
 Test infrastructure.

 How much testing is enough
 Why Testers?

Why Testers?
 Characteristic of a tester
 Curiosity.
 Clear thinking skills.
 Top flight reading speed and comprehension.
 Attention to details.
 Quick learner (outside of testing).

1 testing fundamentals

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