Software testing part

Software Testing TechniquesSoftware Testing Techniques
Preeti MishraPreeti Mishra
Course InstructorCourse Instructor

Observations about
Testing
• “Testing is the process of executing a program
with the intention of finding errors.” – Myers
• “Testing can show the presence of bugs but never
their absence.” - Dijkstra

Good Testing Practices
• A good test case is one that has a high probability
of detecting an undiscovered defect, not one that
shows that the program works correctly
• It is impossible to test your own program
• A necessary part of every test case is a
description of the expected result

Software testing axioms
1. It is impossible to test a program completely.
2. Software testing is a risk-based exercise.
3. Testing cannot show the absence of bugs.
4. The more bugs you find, the more bugs there are.
5. Not all bugs found will be fixed.
6. It is difficult to say when a bug is indeed a bug.
7. Specifications are never final.
8. Software testers are not the most popular members of a
project.
9. Software testing is a disciplined and technical profession.

Characteristics of Testable
Software
• Operable
– The better it works (i.e., better quality), the easier it is to test
• Observable
– Incorrect output is easily identified; internal errors are
automatically detected
• Controllable
– The states and variables of the software can be controlled
directly by the tester
• Decomposable
– The software is built from independent modules that can be
tested independently

Characteristics of Testable
Software (continued)
• Simple
– The program should exhibit functional, structural, and code
simplicity
• Stable
– Changes to the software during testing are infrequent and do
not invalidate existing tests
• Understandable
– The architectural design is well understood; documentation is
available and organized

Test Characteristics
• A good test has a high probability of finding an error
– The tester must understand the software and how it might fail
• A good test is not redundant
– Testing time is limited; one test should not serve the same
purpose as another test
• A good test should be “best of breed”
– Tests that have the highest likelihood of uncovering a whole
class of errors should be used
• A good test should be neither too simple nor too complex
– Each test should be executed separately; combining a series of
tests could cause side effects and mask certain errors

Criteria for Completion
of Testing
• When are we done testing? (Are we there yet?)
• How to answer this question is still a research question
1. One view: testing is never done… the burden simply shifts
from the developer to the customer
2. Or: testing is done when you run out of time or money
3. Or use a statistical model:
− Assume that errors decay logarithmically with testing time
− Measure the number of errors in a unit period
− Fit these measurements to a logarithmic curve
− Can then say: “with our experimentally valid statistical
model we have done sufficient testing to say that with 95%
confidence the probability of 1000 CPU hours of failure
free operation is at least 0.995”

White-box TestingWhite-box Testing

White-box Testing
• Uses the control structure part of component-level design
to derive the test cases
• These test cases
– Guarantee that all independent paths within a module have
been exercised at least once
– Exercise all logical decisions on their true and false sides
– Execute all loops at their boundaries and within their
operational bounds
– Exercise internal data structures to ensure their validity
“Bugs lurk in corners and congregate at boundaries”

Black-box TestingBlack-box Testing

Black-box Testing
• Complements white-box testing by uncovering different
classes of errors
• Focuses on the functional requirements and the information
domain of the software
• Used during the later stages of testing after white box
testing has been performed
• The tester identifies a set of input conditions that will fully
exercise all functional requirements for a program
• The test cases satisfy the following:
– Reduce, by a count greater than one, the number of additional
test cases that must be designed to achieve reasonable testing
– Tell us something about the presence or absence of classes of
errors, rather than an error associated only with the specific
task at hand

Black-box Testing
Categories
• Incorrect or missing functions
• Interface errors
• Errors in data structures or external data base access
• Behavior or performance errors
• Initialization and termination errors

Questions answered by
Black-box Testing
• How is functional validity tested?
• How are system behavior and performance tested?
• What classes of input will make good test cases?
• Is the system particularly sensitive to certain input values?
• How are the boundary values of a data class isolated?
• What data rates and data volume can the system tolerate?
• What effect will specific combinations of data have on
system operation?

Traditional Testing v/sTraditional Testing v/s
Object OrientedObject Oriented
TestingTesting

Levels of Testing
• Testing Levels
• Irrespective of using any software development
paradigm, testing is performed at four important
levels

Unit Testing
• A unit is a smallest testable part of an application.
• In conventional/procedural programming, a unit may be
– an individual program,
– module,
– function,
– procedure
• while in object-oriented programming, the smallest unit
is
– a encapsulated class, which may belong to a base/super class,
abstract class or derived/child class.

Integration Testing
• After the units are individually tested successfully, the
next level of testing i.e integration testing proceeds.
• Integration testing in conventional software
development:
– is to progressively integrate the tested units either
incrementally or non-incrementally, so as to check whether the
software units in an integrated mode are working properly.
• In an object-oriented software development:
– Integrated testing is to verify the interaction among classes
(interclass).
– The relationships among classes are the basic characteristics of
an object-oriented system and define the nature of interaction
among classes and objects
at runtime.

System Testing(Validation Testing)
• Validation testing is followed by integration testing.
Validation testing focuses on user-visible actions and
• It demonstrates conformity with requirements.
• Black-box testing is a testing type used for validation
purpose. Since black-box testing is used for validating the
functionality of software, it is otherwise called as
functional testing.
• Equivalence partitioning and Boundary value analysis are
the two broad categories of black-box testing.

System Testing(Validation Testing)
• There is no distinction among conventional, object-
oriented with respect to validation testing
• System testing verifies that all elements (hardware,
people, databases) are integrated properly so as to ensure
• whether the overall product met its requirement and
achieved the expected performance.
• System testing also deals with non-functional
requirements of the software such as recovery testing,
security testing, stress testing and performance testing.

Object OrientedObject Oriented
TestingTesting

Object-Oriented Testing
• When should testing begin?
• Analysis and Design:
− Testing begins by evaluating the OOA and OOD models
− How do we test OOA models (requirements and use cases)?
− How do we test OOD models (class and sequence diagrams)?
− Structured walk-throughs, prototypes
− Formal reviews of correctness, completeness and consistency
• Programming:
− How does OO make testing different from procedural programming?
− Concept of a ‘unit’ broadens due to class encapsulation
− Integration focuses on classes and their context of a use case
scenario
or their execution across a thread
− Validation may still use conventional black box methods

Testing OO Code
Class testsClass tests IntegrationIntegration
teststests
ValidationValidation
teststests
SystemSystem
teststests

Class (Unit) Testing
• Smallest testable unit is the encapsulated class
• Test each operation as part of a class hierarchy
because its class hierarchy defines its context of use
• Approach:
− Test each method (and constructor) within a class
− Test the state behavior (attributes) of the class between
methods
• class testing focuses on each method, then designing
sequences of methods to exercise states of a class
• But white-box testing can still be applied

Class Testing Process
classclass
to beto be
testedtested
test casestest cases
resultsresults
softwaresoftware
engineerengineer
How to test?How to test?
Why aWhy a
loop?loop?

Class Test Case Design
1. Identify each test case uniquely
- Associate test case explicitly with the class and/or method to
be tested
2. State the purpose of the test
3. Each test case should contain:
a. A list of messages and operations that will be exercised as a
consequence of the test
b. A list of exceptions that may occur as the object is tested
c. A list of external conditions for setup (i.e., changes in the
environment external to the software that must exist in
order to properly conduct the test)
d. Supplementary information that will aid in understanding or
implementing the test
− Automated unit testing tools facilitate these
requirements

Challenges of Class Testing
• Encapsulation:
− Difficult to obtain a snapshot of a class without building
extra methods which display the classes’ state
• Inheritance and polymorphism:
− Each new context of use (subclass) requires re-testing
because a method may be implemented differently
(polymorphism).
− Other unaltered methods within the subclass may use
the redefined method and need to be tested
• White box tests:
− Basis path, condition, data flow and loop tests can all
apply to individual methods, but don’t test interactions
between methods

Random Class Testing
1. Identify methods applicable to a class
2. Define constraints on their use – e.g. the class must always be
initialized first
3. Identify a minimum test sequence – an operation sequence that
defines the minimum life history of the class
4. Generate a variety of random (but valid) test sequences – this
exercises more complex class instance life histories
• Example:
1. An account class in a banking application has open, setup, deposit,
withdraw, balance, summarize and close methods
2. The account must be opened first and closed on completion
3. Open – setup – deposit – withdraw – close
4. Open – setup – deposit –* [deposit | withdraw | balance |
summarize] – withdraw – close. Generate random test sequences
using this template

Integration Testing
• OO does not have a hierarchical control structure
so conventional top-down and bottom-up
integration tests have little meaning
• Integration applied three different incremental
strategies:
− Thread-based testing: integrates classes required to
respond to one input or event
− Use-based testing: integrates classes required by one
use case
− Cluster testing: integrates classes required to
demonstrate one collaboration
• What integration testing strategies will you use?

Thread based v/s Use based
• Thread-based testing, integrates the set of classes
required to respond to one
• input or event for the system. Each thread is integrated
and tested individually. Regression testing is applied to
ensure that no side effects occur.
• Use-based testing, begins the construction of the system
by testing those classes (called independent classes) that
use very few of server classes.
• After the independent classes are tested,the dependent
classes that use the independent classes are tested. This
sequence of testing layers of dependent
• classes continues until the entire system is constructed

System/ Validation
Testing
• Are we building the right product?
• Validation succeeds when software functions in a manner
that can be reasonably expected by the customer.
• Focus on user-visible actions and user-recognizable
outputs
• Details of class connections disappear at this level
• Apply:
− Use-case scenarios from the software requirements spec
− Black-box testing to create a deficiency list
− Acceptance tests through alpha (at developer’s site) and beta (at
customer’s site) testing with actual customers
• How will you validate your term product?

Object-oriented software testing
problems
 Integration testing may add a large cost (time
resources) to software development process.
 Polymorphism - attribute may have more than one
set of values and an operation may be
implemented by more than one method.
 Inheritance - object may have more than one
super class.
 Encapsulation - information hiding.

Performance TestingPerformance Testing

Introduction
• What is Performance Testing?
• Performance testing, a non-functional testing technique performed to
determine the system parameters in terms of responsiveness and
stability under various workload. Performance testing measures the
quality attributes of the system, such as scalability, reliability and
resource usage.
• Attributes of Performance Testing:
– Speed
– Scalability
– Stability
– reliability

Performance Testing Techniques:
– Load testing - It is the simplest form of testing conducted to understand the
behaviour of the system under a specific load. Load testing will result in measuring
important business critical transactions and load on the database, application server,
etc., are also monitored.
– Stress testing - It is performed to find the upper limit capacity of the system and
also to determine how the system performs if the current load goes well above the
expected maximum.
– Soak testing - Soak Testing also known as endurance testing, is performed to
determine the system parameters under continuous expected load. During soak tests
the parameters such as memory utilization is monitored to detect memory leaks or
other performance issues. The main aim is to discover the system's performance
under sustained use.
– Spike testing - Spike testing is performed by increasing the number of users
suddenly by a very large amount and measuring the performance of the system. The
main aim is to determine whether the system will be able to sustain the workload.

Basics
• Stress testing is a software testing activity that
determines
– the robustness of software by testing beyond the limits
of normal operation.
• Stress testing is particularly important for "mission
critical" software, but is used for all types of
software.

Introduction
• It is a type of non-functional testing.
• It involves testing beyond normal operational capacity, often
to a breaking point, in order to observe the results.
• It is a form of software testing that is used to determine
the stability of a given system.
• It put greater emphasis on robustness, availability, and
error handling under a heavy load, rather than on what would
be considered correct behavior under normal circumstances.
• The goals of such tests may be to ensure the software does
not crash in conditions of insufficient computational
resources (such as memory or disk space).

Load test v/s Stress Test
• Stress testing tries to break the system under test by
overwhelming its resources or by taking resources away
from it (in which case it is sometimes called negative
testing). The main purpose of this process is to make sure
that the system fails and recovers gracefully—a quality
known as recoverability.
• Load testing implies a controlled environment moving from
low loads to high.
• Stress testing focuses on more random events, chaos and
unpredictability.

Reason behind Stress Testing
• The software being tested is "mission critical", that is,
failure of the software (such as a crash) would have
disastrous consequences.
• The amount of time and resources dedicated to testing
is usually not sufficient, with traditional testing
methods, to test all of the situations in which the
software will be used when it is released.

• Even with sufficient time and resources for writing
tests, it may not be possible to determine before hand
all of the different ways in which the software will be
used. This is particularly true for operating systems and
middleware, which will eventually be used by software
that doesn't even exist at the time of the testing.
• Customers may use the software on computers that have
significantly fewer computational resources (such as
memory or disk space) than the computers used for
testing.

• Concurrency is particularly difficult to test with
traditional testing methods. Stress testing may be
necessary to find race conditions and deadlocks.
• Software such as web servers that will be accessible
over the Internet may be subject to denial of service
attacks.
• Under normal conditions, certain types of bugs, such as
memory leaks, can be difficult to detect over the short
periods of time in which testing is performed. However,
these bugs can still be potentially serious. In a sense,
stress testing for a relatively short period of time can
be seen as simulating normal operation for a longer
period of time.

Scalability TestingScalability Testing

Introduction
• What is Scalability Testing?
– Scalability, a performance testing parameter that investigates a
system's ability to grow by increasing the workload per user, or the
number of concurrent users, or the size of a database.
• Scalability Testing Attributes:
– Response Time
– Throughput
– Hits per second, Request per seconds, Transaction per seconds
– Performance measurement with number of users
– Performance measurement under huge load
– CPU usage, Memory usage while testing in progress
– Network Usage - data sent and received
– Web server - Request and response per second

Software testing part

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