chapter 11, testing

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Chapter 11, Testing

Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 2

Terminology

• Failure: Any deviation of the observed behavior from the specified behavior

• Erroneous state (error): The system is in a state such that further processing by the system can lead to a failure

• Fault: The mechanical or algorithmic cause of an error (“bug”)

• Validation: Activity of checking for deviations between the observed behavior of a system and its specification.


Examples of Faults and Errors

• Faults in the Interface specification

• Mismatch between what the client needs and what the server offers

• Mismatch between requirements and implementation

• Algorithmic Faults • Missing initialization• Incorrect branching

condition• Missing test for null

• Mechanical Faults (very hard to find)

• Operating temperature outside of equipment specification

• Errors• Null reference errors• Concurrency errors• Exceptions.


Another View on How to Deal with Faults

• Fault avoidance• Use methodology to reduce complexity • Use configuration management to prevent inconsistency• Apply verification to prevent algorithmic faults• Use Reviews

• Fault detection• Testing: Activity to provoke failures in a planned way• Debugging: Find and remove the cause (Faults) of an

observed failure• Monitoring: Deliver information about state => Used

during debugging• Fault tolerance

• Exception handling• Modular redundancy.


Taxonomy for Fault Handling Techniques

Fault Handling

Fault Avoidance

Fault Detection

Fault Tolerance

Verification

ConfigurationManagementMethodology Atomic

TransactionsModular

Redundancy

System Testing

IntegrationTesting

UnitTesting

Testing Debugging


Observations

• It is impossible to completely test any nontrivial module or system

• Practical limitations: Complete testing is prohibitive in time and cost

• Theoretical limitations: e.g. Halting problem• “Testing can only show the presence of bugs,

not their absence” (Dijkstra). • Testing is not for free

=> Define your goals and priorities


Testing takes creativity

• To develop an effective test, one must have:• Detailed understanding of the system• Application and solution domain knowledge • Knowledge of the testing techniques• Skill to apply these techniques

• Testing is done best by independent testers• We often develop a certain mental attitude that the

program should behave in a certain way when in fact it does not

• Programmers often stick to the data set that makes the program work

• A program often does not work when tried by somebody else.


Testing Activities

UnitTesting

AcceptanceTesting

IntegrationTesting

SystemTesting

RequirementsAnalysis

Document

ClientExpectation

SystemDesign

Document

ObjectDesign

Document

Developer Client

UnitTesting

AcceptanceTesting

IntegrationTesting

SystemTesting


Types of Testing

• Unit Testing• Individual component (class or subsystem)• Carried out by developers• Goal: Confirm that the component or subsystem is

correctly coded and carries out the intended functionality

• Integration Testing• Groups of subsystems (collection of subsystems) and

eventually the entire system• Carried out by developers• Goal: Test the interfaces among the subsystems.

UnitTesting

AcceptanceTesting

IntegrationTesting

SystemTesting


Types of Testing continued...

• System Testing• The entire system• Carried out by developers• Goal: Determine if the system meets the requirements

(functional and nonfunctional)• Acceptance Testing

• Evaluates the system delivered by developers• Carried out by the client. May involve executing typical

transactions on site on a trial basis• Goal: Demonstrate that the system meets the

requirements and is ready to use.

UnitTesting

AcceptanceTesting

IntegrationTesting

SystemTesting


When should you write a test?

• Traditionally after the source code is written

• In XP before the source code written• Test-Driven Development Cycle

• Add a test• Run the automated tests

=> see the new one fail• Write some code• Run the automated tests

=> see them succeed• Refactor code.


Unit Testing

• Static Testing (at compile time)• Review

• Walk-through (informal)• Code inspection (formal)

• Dynamic Testing (at run time)• Black-box testing• White-box testing.

UnitTesting

AcceptanceTesting

IntegrationTesting

SystemTesting


Black-box testing

• Focus: I/O behavior • If for any given input, we can predict the output, then

the component passes the test• Goal: Reduce number of test cases by

equivalence partitioning:• Divide input conditions into equivalence classes• Choose test cases for each equivalence class.

UnitTesting

AcceptanceTesting

IntegrationTesting

SystemTesting


Black-box testing: Test case selection

a) Input is valid across range of values • Developer selects test cases from 3 equivalence classes:

• Below the range• Within the range• Above the range

b) Input is only valid if it is a member of a discrete set

• Developer selects test cases from 2 equivalence classes:• Valid discrete values• Invalid discrete values


Black box testing: An examplepublic class MyCalendar {

public int getNumDaysInMonth(int month, int year) throws InvalidMonthException

{ … }}Representation for month:

1: January, 2: February, …., 12: December

Representation for year:1904, … 1999, 2000,…, 2006, …

How many test cases do we need for the black box testing of getNumDaysInMonth()?


Black box testing: Gregorian Calendar• Month parameter equivalence classes

• 30 days• 31 days• February• No month 0, 13, -1 [throw exception]

• Year parameter equivalence classes• Normal year• Leap year:

• /4• /100• /400


White-box testing overview• Code coverage

• Branch coverage

• Condition coverage

• Path coverage

UnitTesting

AcceptanceTesting

IntegrationTesting

SystemTesting


if ( i = TRUE) printf("YES\n"); else printf("NO\n");Test cases: 1) i = TRUE; 2) i = FALSE

White-box Testing (Continued)• Statement Testing (Algebraic Testing): Test single

statements (Choice of operators in polynomials, etc)

• Loop Testing:• Cause execution of the loop to be skipped completely.

(Exception: Repeat loops)• Loop to be executed exactly once• Loop to be executed more than once

• Path testing:• Make sure all paths in the program are executed

• Branch Testing (Conditional Testing): Make sure that each possible outcome from a condition is tested at least once


/*Read in and sum the scores*/

White-box Testing ExampleFindMean(float Mean, FILE ScoreFile) { SumOfScores = 0.0; NumberOfScores = 0; Mean = 0; Read(ScoreFile, Score); while (! EOF(ScoreFile) {

if ( Score > 0.0 ) { SumOfScores = SumOfScores + Score;

NumberOfScores++; }

Read(ScoreFile, Score); } /* Compute the mean and print the result */ if (NumberOfScores > 0 ) { Mean = SumOfScores/NumberOfScores;

printf("The mean score is %f \n", Mean); } else

printf("No scores found in file\n");}


White-box Testing Example: Determining the Paths

FindMean (FILE ScoreFile){ float SumOfScores = 0.0;

int NumberOfScores = 0; float Mean=0.0; float Score;Read(ScoreFile, Score);while (! EOF(ScoreFile) {

if (Score > 0.0 ) {SumOfScores = SumOfScores + Score;NumberOfScores++;}

Read(ScoreFile, Score);}/* Compute the mean and print the result */if (NumberOfScores > 0) {

Mean = SumOfScores / NumberOfScores;printf(“ The mean score is %f\n”, Mean);

} elseprintf (“No scores found in file\n”);

}

1

23

4

5

7

6

8

9


Constructing the Logic Flow DiagramStart

2

3

4 5

6

7

8 9

Exit

1

F

T F

T F

T


Finding the Test CasesStart

2

3

4 5

6

7

8 9

Exit

1

b

d e

gf

i j

hc

k l

a (Covered by any data)

(Data set must

(Data set must contain at least one value)

be empty)

(Total score > 0.0)(Total score < 0.0)

(Positive score) (Negative score)

(Reached if either f or e is reached)


Test Cases

• Test case 1 : ? (To execute loop exactly once)• Test case 2 : ? (To skip loop body)• Test case 3: ?,? (to execute loop more than

once)

These 3 test cases cover all control flow paths


Unit Testing Heuristics

1. Create unit tests when object design is completed

• Black-box test: Test the functional model

• White-box test: Test the dynamic model

2. Develop the test cases • Goal: Find effective num-

ber of test cases3. Cross-check the test cases

to eliminate duplicates• Don't waste your time!

4. Desk check your source code• Sometimes reduces testing

time5. Create a test harness

• Test drivers and test stubs are needed for integration testing

6. Describe the test oracle• Often the result of the first

successfully executed test7. Execute the test cases

• Re-execute test whenever a change is made (“regression testing”)

8. Compare the results of the test with the test oracle

• Automate this if possible.


JUnit: Overview• A Java framework for writing and running unit tests

• Test cases and fixtures • Test suites• Test runner

• Written with “test first” and pattern-based development in mind

• Tests written before code• Allows for regression testing• Facilitates refactoring

• JUnit is Open Source• www.junit.org• JUnit Version 4, released Mar 2006

UnitTesting

AcceptanceTesting

IntegrationTesting

SystemTesting

http://wwwbruegge.informatik.tu-muenchen.de/twiki/bin/view/Lehrstuhl/KMinSESoSe2007


*

JUnit ClassesTest

run(TestResult)

ConcreteTestCase

setUp()tearDown()runTest()

TestResult

TestCase

run(TestResult)setUp()tearDown()

testName:String

runTest()

TestSuite

run(TestResult)addTest()

UnitToBeTested

Methods under Test


An example: Testing MyList

• Unit to be tested• MyList

• Methods under test• add()• remove()• contains()• size()

• Concrete Test case• MyListTestCase


Test

run(TestResult)

MyListTestCase

setUp()tearDown()runTest()testAdd()testRemove()

TestResult

TestCase


testName:String

runTest()

TestSuite


MyList

add()remove()contains()size()

*


Writing TestCases in JUnitpublic class MyListTestCase extends TestCase {

public MyListTestCase(String name) {super(name);

}public void testAdd() { // Set up the test

List aList = new MyList();String anElement = “a string”;

// Perform the testaList.add(anElement);

// Check if test succeededassertTrue(aList.size() == 1);assertTrue(aList.contains(anElement));

}protected void runTest() {

testAdd();}}

Test

run(TestResult)

MyListTestCase

setUp()tearDown()runTest()testAdd()testRemove()

TestResult

TestCase


testName:String

runTest()

TestSuite


MyList

add()remove()contains()size()

*


Writing Fixtures and Test Casespublic class MyListTestCase extends TestCase {// …private MyList aList;private String anElement;public void setUp() {

aList = new MyList();anElement = “a string”;

}

public void testAdd() {aList.add(anElement);assertTrue(aList.size() == 1);assertTrue(aList.contains(anElement));

}

public void testRemove() {aList.add(anElement);aList.remove(anElement);assertTrue(aList.size() == 0);assertFalse(aList.contains(anElement));

}

Test Fixture

Test Case

Test Case


Collecting TestCases into TestSuitespublic static Test suite() {

TestSuite suite = new TestSuite();suite.addTest(new MyListTest(“testAdd”));suite.addTest(new MyListTest(“testRemove”));return suite;

}Test

run(TestResult)

TestCase


testName:String

runTest()

TestSuite


Composite Pattern!

*


Design patterns in JUnitTest

run(TestResult)

ConcreteTestCase


TestResult

TestCase


testName:String

runTest()

TestSuite


Command Pattern

CompositePattern

Adapter Pattern

TestedUnit

*

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Overview

• Integration testing• Big bang• Bottom up• Top down• Sandwich• Continuous

• System testing• Functional• Performance

• Acceptance testing• Summary


Integration Testing

• The entire system is viewed as a collection of subsystems (sets of classes) determined during the system and object design

• Goal: Test all interfaces between subsystems and the interaction of subsystems

• The Integration testing strategy determines the order in which the subsystems are selected for testing and integration.


Why do we do integration testing?

• Unit tests only test the unit in isolation

• Many failures result from faults in the interaction of subsystems

• Often many Off-the-shelf components are used that cannot be unit tested

• Without integration testing the system test will be very time consuming

• Failures that are not discovered in integration testing will be discovered after the system is deployed and can be very expensive.


Stubs and drivers

• Driver:• A component, that calls the TestedUnit• Controls the test cases

• Stub:• A component, the TestedUnit

depends on• Partial implementation• Returns fake values.

Driver

TestedUnit

Stub


Example: A 3-Layer-Design

Layer I

Layer II

Layer III

SpreadSheetView

A

Calculator

C

BinaryFileStorage

E

XMLFileStorage

F

CurrencyDataBase

G

CurrencyConverter

D

DataModel

B

A

C

E F G

DB

SpreadSheetView

BinaryFileStorage

EntityModel

A

E F

CurrencyDataBase

G

CurrencyConverter

DB

Calculator

C

XMLFileStorage

(Spreadsheet)


A

C

E F G

DB

Big-Bang Approach

Test A

Test B

Test G

Test F

Test E

Test C

Test DTest

A, B, C, D,E, F, G

Unit tests each of the subsystems, and then does one gigantic integration test, in which all the subsystems are immediately tested together.

Not so good. Why?


Big Bang Approach

• Pro• Easy• No additional test drivers and stubs are needed

• Con• Impossible to distinguish failures in the interface from

the failures within a component• Difficult to pinpoint the specific component responsible

for the failure


Bottom-up Testing Strategy• The subsystems in the lowest layer of the call

hierarchy are tested individually• Then the next subsystems are tested that call the

previously tested subsystems• This is repeated until all subsystems are included• Drivers are needed.


A

C

E F G

DB

Bottom-up Integration A

Test A, B, C, D,

E, F, G

ETest E

F

Test F

B

Test B, E, F

C

Test C

D

Test D,G

G

Test G

Test D


Bottom-up

• Pro:• Simple

• Con:• Subsystem interfaces are not tested

• Impossible to distinguish failures in interfaces from failures within a component

• Difficult to pinpoint the specific component responsible for the failure


Pros and Cons of Bottom-Up Integration Testing• Con:

• Tests the most important subsystem (user interface) last

• Drivers needed• Pro

• No stubs needed• Useful for integration testing of the following systems

• Object-oriented systems• Real-time systems• Systems with strict performance requirements.


Top-down Testing Strategy

• Test the top layer or the controlling subsystem first

• Then combine all the subsystems that are called by the tested subsystems and test the resulting collection of subsystems

• Do this until all subsystems are incorporated into the test

• Stubs are needed to do the testing.


Top-down Integration

Test A, B, C, D,

E, F, G

All LayersLayer I + II

Test A, B, C, D

Layer I

Test A

A

E F

B C D

G


Pros and Cons of Top-down Integration TestingPro• Test cases can be defined in terms of the

functionality of the system (functional requirements)

• No drivers needed

Cons• Writing stubs is difficult: Stubs must allow all

possible conditions to be tested.• Large number of stubs may be required,

especially if the lowest level of the system contains many methods.

• Some interfaces are not tested separately.


Sandwich Testing Strategy

• Combines top-down strategy with bottom-up strategy

• The system is viewed as having three layers• A target layer in the middle• A layer above the target• A layer below the target

• Testing converges at the target layer.


Sandwich Testing Strategy

Test A, B, C, D,

E, F, GTest B, E, F

Test D,G

Test A

Test E

Test F

Test G

Test A,B,C, D

A

E F

B C D

G


Pros and Cons of Sandwich Testing

• Top and Bottom Layer Tests can be done in parallel

• Problem: Does not test the individual subsystems and their interfaces thoroughly before integration

• Solution: Modified sandwich testing strategy


Modified Sandwich Testing Strategy

• Test in parallel:• Middle layer with drivers and stubs• Top layer with stubs• Bottom layer with drivers

• Test in parallel:• Top layer accessing middle layer (top layer

replaces drivers)• Bottom accessed by middle layer (bottom

layer replaces stubs).


Modified Sandwich Testing

Test F

Test E

Test B

Test G

Test D

Test A

Test C

Test B, E, F

Test D,G

Test A,C

Test A, B, C, D,

E, F, G

A

E F

B C D

G


Continuous Testing

• Continuous build:• Build from day one• Test from day one• Integrate from day one System is always runnable

• Requires integrated tool support:• Continuous build server• Automated tests with high coverage• Tool supported refactoring• Software configuration management• Issue tracking.


SpreadSheetView

BinaryFileStorage

DataModel

Continuous Testing Strategy

Layer I

Layer II

Layer III

A

E F

CurrencyDataBase

G

CurrencyConverter

DB

Calculator

C

XMLFileStorage

Sheet View + Cells+ Addition + File Storage


Steps in Integration Testing

.

1. Based on the integration strategy, select a component to be tested. Unit test all the classes in the component.

2. Put selected component together; do any preliminary fix-up necessary to make the integration test operational (drivers, stubs)

3. Test functional requirements: Define test cases that exercise all use cases with the selected component

4. Test subsystem decomposition: Define test cases that exercise all dependencies

5. Test non-functional requirements: Execute performance tests

6. Keep records of the test cases and testing activities.

7. Repeat steps 1 to 7 until the full system is tested.

The primary goal of integration testing is to identify failures with the (current) component configuration.


System Testing

• Functional Testing• Validates functional requirements

• Performance Testing• Validates non-functional requirements

• Acceptance Testing• Validates clients expectations

UnitTesting

AcceptanceTesting

IntegrationTesting

SystemTesting


.

Functional Testing

Goal: Test functionality of system• Test cases are designed from the requirements

analysis document (better: user manual) and centered around requirements and key functions (use cases)

• The system is treated as black box• Unit test cases can be reused, but new test

cases have to be developed as well.


Performance Testing

Goal: Try to violate non-functional requirements• Test how the system behaves when overloaded.

• Can bottlenecks be identified? (First candidates for redesign in the next iteration)

• Try unusual orders of execution • Call a receive() before send()

• Check the system’s response to large volumes of data

• If the system is supposed to handle 1000 items, try it with 1001 items.

• What is the amount of time spent in different use cases?

• Are typical cases executed in a timely fashion?


Types of Performance Testing• Stress Testing

• Stress limits of system• Volume testing

• Test what happens if large amounts of data are handled

• Configuration testing• Test the various software and

hardware configurations • Compatibility test

• Test backward compatibility with existing systems

• Timing testing• Evaluate response times and

time to perform a function

• Security testing• Try to violate security

requirements• Environmental test

• Test tolerances for heat, humidity, motion

• Quality testing• Test reliability, maintain-

ability & availability • Recovery testing

• Test system’s response to presence of errors or loss of data

• Human factors testing• Test with end users.


Acceptance Testing

• Goal: Demonstrate system is ready for operational use

• Choice of tests is made by client

• Many tests can be taken from integration testing

• Acceptance test is performed by the client, not by the developer.

• Alpha test:• Client uses the software

at the developer’s environment.

• Software used in a controlled setting, with the developer always ready to fix bugs.

• Beta test:• Conducted at client’s

environment (developer is not present)

• Software gets a realistic workout in target environment


Testing has many activities

Establish the test objectives

Design the test cases

Write the test cases

Test the test cases

Execute the tests

Evaluate the test results

Change the system

Do regression testing


Test Team

Test

Analyst

TeamUser

Programmertoo familiarwith code

ProfessionalTester

Configuration Management

Specialist

System Designer


The 4 Testing Steps

1. Select what has to be tested• Analysis: Completeness of

requirements• Design: Cohesion• Implementation: Source

code2. Decide how the testing is

done• Review or code inspection• Proofs (Design by Contract)• Black-box, white box, • Select integration testing

strategy (big bang, bottom up, top down, sandwich)

3. Develop test cases• A test case is a set of test

data or situations that will be used to exercise the unit (class, subsystem, system) being tested or about the attribute being measured

4. Create the test oracle• An oracle contains the

predicted results for a set of test cases

• The test oracle has to be written down before the actual testing takes place.


Guidance for Test Case Selection• Use analysis knowledge

about functional requirements (black-box testing):

• Use cases• Expected input data• Invalid input data

• Use design knowledge about system structure, algorithms, data structures (white-box testing):

• Control structures• Test branches,

loops, ...• Data structures

• Test records fields, arrays, ...

• Use implementation knowledge about algorithms and datastructures:

• Force a division by zero• If the upper bound of an

array is 10, then use 11 as index.


Summary

• Testing is still a black art, but many rules and heuristics are available

• Testing consists of• Unit testing• Integration testing• System testing• Acceptance testing

• Design patterns can be used for integration testing

• Testing has its own lifecycle

chapter 11, testing

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