lecture 06 testing

SWENG 580: Advanced Software Engineering

© Penn State UniversityLast updated: Friday, April 28, 2023

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Software Testing

Objectives and principlesTechniques

ProcessObject-oriented testing

Test workbenches and frameworks


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Lecture ObjectivesUnderstand

Software testing objectives and principles Testing techniques – black-box and white-box Testing process – unit and integration Object-oriented testing Test workbenches and frameworks


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Can We Exhaustively Test Software?

There are 250 billion unique paths between A and B. If each set of possible data is used, and a single run takes 1 millisecond to execute, it would take 8 years to test all paths.

less than8 cycles

less than8 cycles

less than8 cycles

less than8 cycles

A

B


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Can we test all types of software bugs?

Software testing is mainly suitable for dealing with faults that consistently define themselves under well defined conditions

Such faults are called Bohrbugs (an allusion to Niels Bohr’s simple and intelligible atomic model) Testers do encounter failures they can’t reproduce.

Under seemingly exact conditions, the actions that a test case specifies can sometimes, but not always, lead to a failure

Software engineers sometimes refer to faults with this property as Mandelbugs (an allusion to Benoit Mandelbrot, a leading researcher in fractal geometry)

Example: the software fault in the Patriot missile defense system responsible for the Scud incident in Dhahran

To project a target’s trajectory, the weapons control computer required its velocity and the time as real values The system, however, kept time internally as an integer, counting tenths of seconds and storing them in a 24

bit register The necessary conversion into a real value caused imprecision in the calculated range where a detected target

was expected next For a given velocity of the target, these inaccuracies were proportional to the length of time the system had

been continuously running


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Testing Objectives Software testing can show the presence of bugs,

but it can never show their absence. Therefore, Testing is the process of exercising a program with

the specific intent of finding errors prior to delivery to the end user.

A good test case is one that has a high probability of finding an error.

A successful test is one that uncovers an error.


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Testing Principles All tests should be traceable to customer requirements Tests should be planned long before testing begins The Pareto principle applies to software testing Testing should begin “in the small” and progress toward

testing “in the large” Exhaustive testing is not possible To be most effective, testing should be conducted by an

independent third party


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Test Case Design Testing must be planned and performed

systematically…not ad hoc or random. Testing can be performed in two ways:

1. Knowing the specified function that a product has been designed to perform – black-box testing.

2. Knowing the internal workings of the product and testing to ensure all parts are exercised adequately – white-box testing.


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Black-box TestingAn approach to testing where the program is

considered as a ‘black-box’The program test cases are based on the

system specification Test planning can begin early in the

software process


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Equivalence PartitioningDivide the input domain into classes of data

from which test cases can be derived.Strives to define a test that uncovers

classes of errors – reducing total number of test cases required.


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Example… Specifications for DBMS state that product must handle

any number of records between 1 and 16,383 (2 14 –1) If system can handle 34 records and 14,870 records,

then probably will work fine for 8,252 records, say. If system works for any one test case in range

(1..16,383), then it will probably work for any other test case in range

Range (1..16,383) constitutes an equivalence class Any one member is as good a test case as any other member

of the class


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…ExampleRange (1..16,383) defines three different

equivalence classes: Equivalence Class 1: Fewer than 1 record Equivalence Class 2: Between 1 and 16,383

records Equivalence Class 3: More than 16,383

records


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Boundary Value AnalysisTechnique that leads to selection of test

cases that exercise bounding values.Selecting test case on or just to one side of

boundary of equivalence class increases probability of detecting fault.

"Bugs lurk in corners and congregate at boundaries"


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DBMS Example Test case 1: 0 records Member of equivalence class 1 (&

adjacent to boundary value) Test case 2: 1 record Boundary value Test case 3: 2 records Adjacent to boundary value Test case 4: 723 records Member of equivalence class 2 Test case 5: 16,382 records Adjacent to boundary value Test case 6: 16,383 records Boundary value Test case 7: 16,384 records Member of equivalence class 3

(& adjacent to boundary value)


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BVA of Output SpecsExample In 1994, minimum Social Security (FICA)

deduction from any one paycheck was $0.00, and the maximum was $3571.20 test cases must include input data which should result

in deductions of exactly $0.00 and exactly $3571.20 test data that might result in deductions of less than

$0.00 or more than $3571.20


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White-box Testing Test case design method that uses the control

structure of the procedural design to derive test cases.

Can derive tests that: Guarantee all independent paths have been exercised at

least once Exercise all logical decisions on their true and false sides Execute all loops at their boundaries and within

operational bounds Exercise internal data structures to ensure validity


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Basis Path TestingProposed by Tom McCabe.Use cyclomatic complexity measure as

guide for defining a basis set of execution paths.

Test cases derived to exercise the basis set are guaranteed to execute every statement at least once.


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CC = 5 So 5 independent paths

1. a, c, f2. a, d, c, f3. a, b, e, f4. a, b, e, a, …5. a, b, e, b, e, …

Independent Paths

a b c d e

f


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Graph Matrices By forming a graph matrix the cyclomatic

complexity and the basis path set can be found automatically.

a b c d e fa 1 1 1b 1c 1d 1e 1 1 1f

3-1 = 21-1 = 01-1 = 01-1 = 03-1 = 2

CC= 2+2+1=5


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The Flowgraph Before the cyclomatic complexity can be calculated, and

the paths determined, the flowgraph must be created. Done by translating the source code into flowgraph

notation:

sequence if while until case


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ExamplePROCEDURE average

INTERFACE RETURNS average, total.input, total.valid;INTERFACE ACCEPTS value, minimum, maximum;

TYPE value[1:100] IS SCALAR ARRAY;TYPE average, total.input, total.valid; minimum, maximum, sum IS SCALAR;TYPE i IS INTEGER;

i = 1;total.input = total.valid = 0;sum = 0;DO WHILE value[i] <> -999 AND total.input < 100

increment total.input by 1;

IF value[i] >= minimum AND value[1] <= maximum

THEN increment total.valid by 1; sum = sum + value[i]ELSE skipENDIFincrement i by 1;

ENDDOIF total.valid > 0

THEN average = sum/total.valid;ELSE average = -999;

ENDIFEND average

1 23

4

56

78

9 101112

13


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…Example 1

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Flowgraph for average

Determine the:1. Cyclomatic complexity

2. Independent paths


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Condition TestingExercises logical conditions contained within

a program module.Types of errors found include;

Boolean operator error (OR, AND, NOT) Boolean variable error Boolean parenthesis error Relational operator error (>,<,=,!=,…) Arithmetic expression error


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Loop TestingFocus exclusively on the validity of loop

constructs.4 types of loop can be defined:

Simple Nested Concatenated Unstructured


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Loop Types

Simple

Concatenated NestedUnstructured


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Simple LoopsWhere n is the max number of passes, the

following test can be applied: Skip loop entirely Only one pass 2 passes m passes (where m<n) n-1, n, n+1 passes


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Nested Loops If the approach for simple loops is extended, number of

possible tests would grow geometrically – impractical. Instead:

Start at innermost loop. Set all other loops to minimum values. Conduct simple loop test for innermost loop while holding

outer loops at minimum loop counter values. Add other test for out-of-range or excluded values.

Work outward, conducting tests for next loop, but keeping all other outer lops at minimum values and other nested loops to ‘typical’ values.

Continue until all loops tested.


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Concatenated LoopsTest as simple loops provided each loop is

independent. If two loops are concatenated and loop

counter for loop 1 is used as initial value for loop 2, then test as nested loops.


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Unstructured LoopsCan’t test unstructured loops effectively.Reflects very bad practice and should be

redesigned.


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The Tester Who does the testing?

a) Developerb) Member of development teamc) SQAd) All of the above


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Independent Test Group Strictly speaking, testing should be performed by an

independent group (SQA or 3rd party) Members of the development team are inclined to

be more interested in meeting the rapidly-approaching due-date.

The developer of the code is prone to test “gently”. Must remember that the objective is to find errors,

not to complete test without finding them (because they’re always there!)


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Successful Testing The success of testing can be measured by applying a

simple metric:

So as defect removal efficiency approaches 1, process approaches perfection.

0.1

DRE

DefectsErrorsErrorsDRE


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The Testing Process Unit testing

Testing of individual program components Often performed by the component developer Tests often derived from the developer’s experience! Increased productivity possible with xUnit framework

Integration testing Testing of groups of components integrated to create

a system or sub-system The responsibility of an independent testing team Tests are based on a system specification


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Testing Phases

Unittesting

Integrationtesting

Software developer Development team/ SQA/Independent Test Group


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Integration Testing Tests complete systems or subsystems

composed of integrated components Integration testing should be black-box testing

with tests derived from the specification Main difficulty is localizing errors Incremental integration testing reduces this

problem


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Incremental Integration Testing

T3

T2

T1

T4

T5

A

B

C

D

T2

T1

T3

T4

A

B

C

T1

T2

T3

A

B

Test sequence1

Test sequence2

Test sequence3


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Approaches to Integration Testing Top-down testing

Start with high-level system and integrate from the top-down replacing individual components by stubs where appropriate

Bottom-up testing Integrate individual components in levels until the

complete system is created In practice, most integration involves a combination of

these strategies


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Top-down Testing

Level 2Level 2Level 2Level 2

Level 1 Level 1Testingsequence

Level 2stubs

Level 3stubs

. . .


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Bottom-up Testing

Level NLevel NLevel NLevel NLevel N

Level N–1 Level N–1Level N–1

Testingsequence

Testdrivers

Testdrivers


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Which is Best? In bottom-up testing:

Test harnesses must be constructed and this takes time.

Integration errors are found later rather than earlier. Systems-level design flaws that could require major

reconstruction are found last. There is no visible, working system until the last stage

so is harder to demonstrate progress to clients.


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Takes place when modules or sub-systems are integrated to create larger systems

Objectives are to detect faults due to interface errors or invalid assumptions about interfaces

Particularly important for object-oriented development as objects are defined by their interfaces

Interface Testing


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Interface TestingTestcases

BA

C


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Interfaces Types Parameter interfaces

Data passed from one procedure to another Shared memory interfaces

Block of memory is shared between procedures Procedural interfaces

Sub-system encapsulates a set of procedures to be called by other sub-systems

Message passing interfaces Sub-systems request services from other sub-systems


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Interface Errors Interface misuse

A calling component calls another component and makes an error in its use of its interface e.g. parameters in the wrong order

Interface misunderstanding A calling component embeds assumptions about the

behaviour of the called component which are incorrect Timing errors

The called and the calling component operate at different speeds and out-of-date information is accessed


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Interface Testing Guidelines Design tests so that parameters to a called

procedure are at the extreme ends of their ranges

Always test pointer parameters with null pointers Use stress testing in message passing systems In shared memory systems, vary the order in

which components are activated Design tests which cause the component to fail


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Stress Testing Exercises the system beyond its maximum design

load. Stressing the system often causes defects to come to light

Stressing the system test failure behaviour. Systems should not fail catastrophically. Stress testing

checks for unacceptable loss of service or data Particularly relevant to distributed systems

which can exhibit severe degradation as a network becomes overloaded


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The components to be tested are object classes that are instantiated as objects

Larger grain than individual functions so approaches to white-box testing have to be extended

No obvious ‘top’ to the system for top-down integration and testing

Object-Oriented Testing


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Testing LevelsTest object classesTest clusters of cooperating objectsTest the complete OO system


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Object Class Testing Complete test coverage of a class involves

Testing all operations associated with an object Setting and interrogating all object attributes Exercising the object in all possible states

Inheritance makes it more difficult to design object class tests as the information to be tested is not localized


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Object Integration Levels of integration are less distinct in object-

oriented systems Cluster testing is concerned with integrating and

testing clusters of cooperating objects Identify clusters using knowledge of the operation

of objects and the system features that are implemented by these clusters


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Approaches to Cluster Testing Use-case or scenario testing

Testing is based on a user interactions with the system Has the advantage that it tests system features as experienced by

users Thread testing

A thread consists of all the classes needed to respond to a single external input. Each class is unit tested, and then the thread set is exercised.

Object interaction testing Tests sequences of object interactions that stop when an object

operation does not call on services from another object Uses-based testing

Begins by testing classes that use few or no server classes. Next, classes that use the first group of classes are tested, followed by classes that use the second group, and so on.


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Scenario-Based Testing Identify scenarios from use-cases and

supplement these with interaction diagrams that show the objects involved in the scenario

Consider the scenario in the weather station system where a report is generated


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Collect Weather Data:CommsController

request (report)

acknowledge ()report ()

summarise ()

reply (report)

acknowledge ()

send (report)

:WeatherStation :WeatherData


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Weather Station Testing Thread of methods executed

CommsController:request WeatherStation:report WeatherData:summarize

Inputs and outputs Input of report request with associated acknowledge

and a final output of a report Can be tested by creating raw data and ensuring that it

is summarized properly Use the same raw data to test the WeatherData object


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OO Testing: Myths & Reality Inheritance means never having to say your

sorry

Reuse means never having to say your sorry

Black box testing is sufficient


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Implications of Inheritance Myth:

specializing from tested superclasses means subclasses will be correct

Reality: Subclasses create new ways to misuse inherited

features Different test cases needed for each context Need to retest inherited methods, even if

unchanged.


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Implications of Reuse Myth:

Reusing a tested class means that the behavior of the server object is trustworthy

Reality: Every new usage provides ways to misuse a

server. Even if many server object of a given class function

correctly, nothing is to prevent a new client class from using it incorrectly

we can't automatically trust a server because it performs correctly for one client


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Implication of Encapsulation Myth:

White-box testing violates encapsulation, surely black-box testing (of class interfaces) is sufficient.

Reality: Studies indicate that “thorough” BBT sometimes

exercises only 1/3 of code. BBT exercises all specified behaviors, what

about unspecified behaviors?! Need to examine implementation.


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And What About Polymorphism?

Each possible binding of a polymorphic component requires separate test…probably separate test case!


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Testing Workbenches Testing is an expensive process phase. Testing

workbenches provide a range of tools to reduce the time required and total testing costs

Most testing workbenches are open systems because testing needs are organization-specific

Difficult to integrate with closed design and analysis workbenches


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A Testing Workbench

Dynamicanalyser

Programbeing tested

Testresults

Testpredictions

Filecomparator

Executionreport Simulator

Sourcecode

Testmanager Test data Oracle

Test datagenerator Specification

Reportgenerator

Test resultsreport


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Workbench Components Test manager: manages the running of program tests Test data generator: selects test data from database or uses patterns

to generate random data of correct form Oracle: Predicts expected results (may be previous version/prototype) Comparator: compare results of oracle and program, or program and

previous version (regression test) Dynamic analyzer: counts number of times each statement is

executed during test. Simulator: simulates environment (target platform, user interaction,

etc)


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xUnit FrameworkDeveloped by Kent BeckMakes object-oriented unit testing more

accessible.Freeware versions available for most object-

oriented languages www.xprogramming.com/software.htm

http://www.xprogramming.com/software.htm


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jUnit – “successful”


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jUnit – “unsuccessful”


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Simple Guide to Using xUnit Subclass TestCase class for the object under test

Ensure test class has scope over object under test.

Add a test method to the test class for each method. An xUnit test method is an ordinary method without parameters.

Code the test case in the test method Creates objects necessary for the test (fixture) (1)

Exercises objects in the fixture (2)

Verifies the result. (3)


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Example – Money class(from Test Infected)

class Money { private int fAmount; private String fCurrency; public Money(int amount, String currency) { fAmount= amount; fCurrency= currency; }

public int amount() { return fAmount; }

public String currency() { return fCurrency; } public Money add(Money m) { return new Money(amount()+m.amount(), currency()); }

}

public class MoneyTest extends TestCase { //… public void testSimpleAdd() { Money m12CHF= new Money(12, "CHF"); // (1) Money m14CHF= new Money(14, "CHF"); Money expected= new Money(26, "CHF"); Money result= m12CHF.add(m14CHF); // (2) Assert.assertTrue(expected.equals(result)); // (3) }}

Requires a way to test that two Money objects are equal

(override equals in Object) but first must write test for equals

in MoneyTest!


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Key PointsExhaustive testing is not possibleTesting must be done systematically using black-box and

white-box testing techniquesTesting must be done at both unit and integration levelsObject-oriented programming offers its own challenges for

testingTesting workbenches and frameworks can help with the

testing process


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ReferencesM. Grottke and K.S. Trivedi. Fighting Bugs: Remove, Retry,

Replicate and Rejuvinate. IEEE Computer, February 2007, pp. 107 – 109.

R. Pressman. Software Engineering: A Practitioners Approach, New York, NY: McGraw-Hill, 6th Ed, 2004.

I. Sommerville. Software Engineering, 6th Ed. New York, NY: Addison-Wesley, 2000.

lecture 06 testing

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