09 testing

COMP 211COMP 211 TESTINGTESTING1

TESTINGTESTINGTESTINGTESTING

COMP 211COMP 211INTRODUCTION TOINTRODUCTION TO

SOFTWARE ENGINEERINGSOFTWARE ENGINEERING

COMP 211COMP 211INTRODUCTION TOINTRODUCTION TO

SOFTWARE ENGINEERINGSOFTWARE ENGINEERING


TESTING OVERVIEWTESTING OVERVIEW [9.1]

testing is the process of finding differences between the specified (expected) and the observed (existing) system behavior

usually done by developers that were not involved in system implementation

to test a system effectively, must have a detailed understanding of the whole system

not a job for novices

it is impossible to completely test a nontrivial system

systems often deployed without being completely tested

Goal:Goal: design tests that will systematically find defects aim is to break the system (make it fail)

Goal:Goal: design tests that will systematically find defects aim is to break the system (make it fail)


the time uncertainty in testing is the debug part!

TESTING OVERVIEWTESTING OVERVIEW [9.2]

Softwareconfiguration

Testconfiguration

Testresults

Expectedresults

Errors

Errorratedata

Corrections

Testing Evaluation

Reliability& quality

model

Debug

Done

No errors


TESTING — VERIFICATION & VALIDATIONTESTING — VERIFICATION & VALIDATION

verification is the process of making sure that we have built the product right (i.e., it meets its stated requirements) most of the testing workflow is targeted at doing verification

validation is the process of making sure that we have built the right product (i.e., it is fit for its purpose) acceptance tests deal mainly with validation

testing verifies the results of implementation by testing each build as well as final versions of the system by– planning the tests required for each iteration

– designing and implementing the tests by creating test cases that specify what to test test procedures that specify how to test test components to automate the testing, if possible


Inception Elaboration Construction Transition

TESTING LIFE CYCLE ROLETESTING LIFE CYCLE ROLE

PhasesCore Workflows

Requirements

Analysis

Design

Implementation

Testing

iter.#1

iter.#2

— — — — —iter.#n-1

iter.#n

Increments

Iter

atio

n


TESTING ARTIFACTS & WORKERSTESTING ARTIFACTS & WORKERS

responsible for

TestEngineer

ComponentEngineer

responsible for

TestCase

XTest

ModelTest

EvaluationTest

Procedure

XTestPlan

XDefect

TestComponent

IntegrationTester

SystemTester

responsible for


UP — TESTING PROCESSUP — TESTING PROCESS

IntegrationTester

TestEngineer

SystemTester

PlanTests

PerformIntegration

Tests

ImplementTests

PerformSystemTests

EvaluateTests

ComponentEngineer

DesignTests

PerformUnit Test


TESTING TRUTHSTESTING TRUTHS

testing cannot show the absence of software errors;it can only show that software errors are present!

unlike software construction,testing is a destructive process–> try to make the software fail

a test is successful only if it uncovers a defect (bug)

hence, good testing has the opposite natureof good software engineering

(i.e., for good software engineering, success –> no defect foundfor good testing, success –> defect found)


It is impossible to completely test the entire system!

PLAN TESTSPLAN TESTS [9.5.1]

Testing strategy: specifies the criteria and goals of testing– what kinds of tests to perform and how to perform them

– the required level of test and code coverage

– the percentage of tests that should execute with a specific result

Estimate of resources required: human/system

Schedule for the testing: when to run which tests

Overall goalOverall goal: design a set of tests that has the highest likelihood of uncovering defects with the minimum amount of time and effort since resources are usually limited (up to 40% of project effort often devoted to testing)

Overall goalOverall goal: design a set of tests that has the highest likelihood of uncovering defects with the minimum amount of time and effort since resources are usually limited (up to 40% of project effort often devoted to testing)


DESIGN TESTSDESIGN TESTS [9.3.2]

test case: one way of testing the system (what, conditions, how)test case: one way of testing the system (what, conditions, how)

knowing the internal workings of a component, design test cases to ensure the component performs according to specification

White Box Testing: “testing-in-the-small”Derive test cases to verify component logic based on data/control structures. –> Availability of source code is required.

knowing the specified functionality of a component, design test cases to demonstrate that the functionality is fully operational

Black Box Testing: “testing-in-the-large”Derive test cases to verify component functionality based on the inputs and outputs. –> Availability of source code is not required!

Regression Testing: selective White Box and Black Box re-testing to ensure that no new defects are introduced after a change


WHITE BOX TESTINGWHITE BOX TESTING

Goal:Goal: ensure that we have executed/exercised:– all independent paths in the code at least once– all logical decisions on their true and false sides– all loops at their boundaries and within their bounds– internal data structures to ensure their validity

Goal:Goal: ensure that we have executed/exercised:– all independent paths in the code at least once– all logical decisions on their true and false sides– all loops at their boundaries and within their bounds– internal data structures to ensure their validity

Why is this important?

logic errors and incorrect assumptions are inversely proportional to a path’s execution probability

errors more likely in less used parts of the code

we often believe that a path is not likely to be executed reality is often counter intuitive

typos are random its likely that untested paths will contain some


There are 1014 possible paths!It takes 3,170 years to exhaustively test the program if each test requires 1 ms!!

WHY NOT EXHAUSTIVE CODE TESTING?WHY NOT EXHAUSTIVE CODE TESTING?

loop < 20 timesHow long would it take to exhaustively test this program?


Even though the False branch executes no additional statements, it needs to be tested!

WHY NOT JUST STATEMENT TESTING?WHY NOT JUST STATEMENT TESTING?

i = j + 1if (A && B {

x = y + z;}n = p + 1;

i = j + 1

A && B

x = y + z

n = p + 1

TrueFalse

suppose we modify the program to:

i = 0if (A && B {

i = 1;}x = y / i;


BASIS PATH TESTINGBASIS PATH TESTING [9.4.2]

GoalGoal: exercise each independent path in the code at least onceGoalGoal: exercise each independent path in the code at least once

1. From the code, draw a corresponding flow graph.

Sequence

If-then-else

...

Case

Do-untilDo-while


BASIS PATH TESTING EXAMPLEBASIS PATH TESTING EXAMPLE

procedure: process records1. do while records remain2. read record;3. if record field 1 = 04. then store in buffer;5. increment counter;6. elseif record field 2 = 07. then reset counter;8. else store in file;9. endif10. endif11. enddo

end


BASIS PATH TESTINGBASIS PATH TESTING

2. Determine the cyclomatic complexity of the flow graph.

cyclomatic complexity: a quantitative measure of thelogical complexity of code

Ways to compute cyclomatic complexity V(G):

V(G) = number of regions (areas bounded by nodes and edges—area outside graph is also a region)

V(G) = number of edges - number of nodes + 2

V(G) = number of (simple) predicate nodes + 1

provides an upper bound on the number of pathsthat need to be tested in the code



3. Determine a basis set of linearly independent paths.

independent path any path that introduces at least one new set of processing statements or a new condition

basis set set of independent paths through the code

test cases derived from a basis set are guaranteed to execute every statement at least one time during testing

basis set is not unique


1-2-3-6-7-9-10-1-11

BASIS PATH TESTING — EXAMPLEBASIS PATH TESTING — EXAMPLE

1-2-3-6-8-9-10-1-11 1-2-3-4-5-10-1-11 1-11

1

91011

2

4

587

3

6



4. Prepare test cases that force the execution of each path in the basis set.

Notes:

you do not need an activity diagram, but the picture will help when you trace component paths

count each logical test—compound tests count as the number of Boolean operators + 1 (i.e., count each simple predicate)

basis path testing should be applied to all components, if possible, and to critical components always

path testing does not test all possible combinations of all paths through the code; it just tests every path at least once


ASU — REGISTER FOR A COURSE PROCEDUREASU — REGISTER FOR A COURSE PROCEDURE

A student can register for a course if he has taken the prerequisites. However, he may not register for a course if he has already taken a course that is an exclusion. A student who does not have the prerequisites can register for a course if he is currently registered in the prerequisite course and has the permission of the instructor. Notwithstanding the preceding, the instructor may waive the prerequisite for a student.

Register for course

If (enrolment is open) AND (student does not have exclusions) AND ((student has prerequisites) OR (student has permission))Registerreturn(success)

Elsereturn(failure)

Endif


IS BASIS PATH TESTING ENOUGH?IS BASIS PATH TESTING ENOUGH?

int Q;. . .i = j + 1;if ( A() && B() ) {

x = y + z;}n = p + 1;. . .

Boolean A() { Boolean B() {if (Flag1) { if (Flag2) {

Q = 0; return TRUE;return TRUE; } else {

} else { int x = 10/Q;return FALSE; return FALSE;

} }} }

i = j + 1

A()&&B()

x = y + z

n = p + 1

TrueFalse

Flag1=FALSE Flag1=TRUEFlag 2=TRUE

What happens when Flag1=TRUE and Flag2=FALSE?

This isThis issufficientsufficientfor basisfor basispath testingpath testing


CONDITION TESTINGCONDITION TESTING

Goal:Goal: further exercises the true and false value of each simple logical condition in the component

Goal:Goal: further exercises the true and false value of each simple logical condition in the component

condition testing

– simple condition: (a rel-op b) where rel-op={<, ≤, =, ≠, ≥, >} (may be negated with NOT), e.g., a≤b; NOT(a≤b)

– compound condition: two or more simple conditions connected with AND, OR, e.g., (a>b) AND (c<d)

– relational expression: (E1 rel-op E2) where E1 and E2 are arithmetic expressions, e.g., ((a*b+c)>(a+b+c))

errors to test for include (incorrect/missing/extra):– Boolean operator – relational operator– Boolean variable – arithmetic expression– Boolean parenthesis


branch testing

for a compound condition C, test true and false branches of C and every simple condition of C

e.g., for C = (a>b) AND (c<d) we test for: C TRUE and FALSEa>b TRUE and FALSEc<d TRUE and FALSE

CONDITION TESTING (cont’d)CONDITION TESTING (cont’d)

domain testing

for an expression E1 rel-op E2, test for E1 greater than, equal to, or less than E2

– guarantees detection of rel-op error if E1 and E2 are correct

– to detect errors in E1 and E2, the difference between E1 and E2 for the tests E1 greater or less than E2 should be as small as possible

– for an expression with n variables, 2n tests are required


Goal:Goal: execute loops at their boundaries and within their boundsGoal:Goal: execute loops at their boundaries and within their bounds

Nested Loops1 conduct simple loop tests for the innermost loop

while holding the outer loops at their minimumiteration

2 work outward, conducting tests for the nextinnermost loop

3 continue until all the loops have been tested

tests grow geometrically as the level of nesting increases

LOOP TESTINGLOOP TESTING

Simple Loops (n iterations)1 skip the loop entirely2 only one pass through the loop3 two passes through the loop4 m passes through the loop where m < n5 n-1, n, n+1 passes through the loop


LOOP TESTING (cont’d)LOOP TESTING (cont’d)

Concatenated Loops independent loops simple loop testing dependent loops nested loop testing

Unstructured Loops redesign!!!


DATA FLOW TESTINGDATA FLOW TESTING

GoalGoal: ensure that the value of a variable is correct at certain points of execution in the code

GoalGoal: ensure that the value of a variable is correct at certain points of execution in the code

select test paths according to the locations ofdefinitions and uses of a variable

DEF(S) = {X | S contains a definition of X} locations of definition of X

USE(S´) = {X | S´ contains a use of X} locations of use of X

Data Use (DU) Chain (X) is the set of [X, S, S´] where X is “live”(i.e., not redefined between S and S´)

one testing strategy: every data use chain must be covered once for every variable, do a test along the path from where the

variable is defined to the statement(s) where the variable is used (can be combined with basis path testing)


BLACK BOX TESTINGBLACK BOX TESTING

black box techniques attempt to find:– incorrect or missing functions– interface errors– data structure or external database access errors– performance errors– initialization and termination errors

Codeinput

actual ? predictedoutput = output

Test cases should:– reduce by more than 1 the number of additional test cases required (i.e.,

a test case should cover a range of input or output values)– tell us something about presence or absence of a class of errors (e.g., all

character data is correctly/incorrectly processed)


all possible input/output values

EQUIVALENCE PARTITIONINGEQUIVALENCE PARTITIONING [9.4.2]

design test cases which are based on valid and invalid inputs/outputs

userqueries

numericaldata output

formatrequests

commandkey input

mousepicks onmenu

responsesto prompts

partition inputs and outputs to create thorough test coverage of a class of errors

partition inputs and outputs to create thorough test coverage of a class of errors


not member of set

SELECTING EQUIVALENCE CLASSESSELECTING EQUIVALENCE CLASSES

1. If input is a range –> one valid and two invalid equivalence classes:

2. If input is a specific value –> one valid and two invalid equivalence classes:

3. If input is a set of related values –> one valid and one invalid class:

4. If input is Boolean –> one valid and one invalid class:

in range greater than rangeless than range

value greater than valueless than value

member of set

BooleannonBoolean


userqueries

SELECTING TEST VALUES — BOUNDARY VALUESSELECTING TEST VALUES — BOUNDARY VALUES[9.4.2]

as well as selecting test data “inside” an equivalence class, we also select data at the “edges” of the equivalence class

numericaldata output

formatrequests

responsesto prompts

commandkey input

mousepicks onmenu

more errors occur at the boundaries of an input/output domain than in the “center”

more errors occur at the boundaries of an input/output domain than in the “center”


not member of set

BOUNDARY VALUE SELECTION — GUIDELINESBOUNDARY VALUE SELECTION — GUIDELINES

1. If the input is a range and is bounded by a and b, then use a, b, and values just above and just below a and b, respectively.

2. If the input is a number of discrete values, use the minimum and the maximum of the values and values just above and just below them, respectively. (Can also be applied to a single specific input value.)

3. For inputs that are a set of values, test all values in the set (if possible) and one value outside the set.

a b

min max

member of set


BOUNDARY VALUE SELECTION — GUIDELINES BOUNDARY VALUE SELECTION — GUIDELINES (cont’d)(cont’d)

5. Apply guidelines 1 and 2 to create output values at the minimum and maximum expected values.

e.g., if the output is a table, create a minimum size table (1 row) and a maximum size table

6. If data structures have boundaries, test these boundary values and values just above and just below them, respectively.

e.g., for an array of bounds 1 to 10 — test array index equal to 0, 1,2, 9, 10, 11

1 100 2 9 11

4. For inputs that are Boolean, test for both Boolean values (T, F) and for a non-Boolean value.

nonBoolean Boolean


Comparison Testing– when reliability is absolutely critical, write several versions of the

software — perhaps to be used as backups– run same test data on all versions; cross-check results for

consistency Caution: if the error is from a bad specification and all

versions are built from the same specification, then the same bug will be present in all copies!

Cause-Effect Graphing1. causes (input conditions) and effects (actions) are identified for a

subsystem2. a cause-effect graph is developed3. the graph is converted to a decision table4. decision table rules are converted into test cases

OTHER BLACK BOX TECHNIQUESOTHER BLACK BOX TECHNIQUES [9.4.2]

Error Guessing– use application domain experience or knowledge to select test values


THREAD TESTINGTHREAD TESTING

event-based approach where tests are based on events which trigger system actions particularly appropriate for object oriented systems

used after classes have been unit tested and integrated into subsystems

need to identify and execute each possible processing thread from use cases

may not be possible to do complete thread testing too many input/output combinations

focus on most commonly exercised threads basic paths through flow of events


THREAD TESTINGTHREAD TESTING

single thread: obj3obj2obj4

obj1

obj3

obj2

obj4

obj5

I1(obj1)

I2(obj1)

I3(obj1)

I1(obj3)

I1(obj2)

O1(obj4)

O2(obj4)

O1(obj5)

multiple thread: obj1obj2{obj5, obj4} multi-input thread: into obj1


STATE-BASED TESTINGSTATE-BASED TESTING [9.4.2]

focuses on comparing the resulting state of a class with the expected state

derive test cases using statechart diagram for a class

derive a representative set of “stimuli” (events) for each transition

check the attributes of the class after applying a “stimuli” to determine of the specified state has been reached

first need to put the class in the desired state before applying the “stimuli”


TEST CASE DOCUMENTATIONTEST CASE DOCUMENTATION

Test case name name of the test case

Description of the test what the test is designed to do

Target class/component/subsystem name name of the thing to be tested

Target class/component/subsystem operation name of the operation to be tested

Test type black box/white box; valid/invalid input

Test value(s) inputs to be used for the test

Verification expected result


IMPLEMENT TESTSIMPLEMENT TESTS

GoalGoal: automate test procedures as much as possibleGoalGoal: automate test procedures as much as possible

running test cases can be very tedious and time consuming– many possible input values and system states to test

test component: a program that automates one or several test procedures or parts of them

there are tools available to help write test components:– perform actions for a test case and the tool “records” the actions

– parameterize the recorded script to accept a variety of input values

spreadsheets and/or database applications can be used to store the required input data and the results of each test


PERFORM TESTS — TESTING STRATEGIESPERFORM TESTS — TESTING STRATEGIES

we need to integrate test cases into a well-planned series of steps that are taken to test a component/subsystem –> test procedure– what are the steps that need to be conducted to test a component?– when are the steps planned and undertaken?– how much effort, time and resources will be required to do the steps?

the testing steps start at the component/subsystem level and work outward toward the integration of the entire system

a testing strategy indicates which testing techniques (white box, black box, thread) are appropriate at which point in time

need to balance:flexibility & creativity with planning & management

testing often occurs when deadline pressures are most severe(progress must be measurable and problems identified as early as possible)


A TESTING STRATEGYA TESTING STRATEGY

Requirements capture R

U Unit testing

AAnalysis

We developthe systemfrom theoutside in

We testthe systemfrom theinside outDDesign

CImplementation(coding)

I Integration testing

SdSystem testing(developer)

ScSystem testing(customer)


Test cases

UNIT TESTINGUNIT TESTING [9.4.2]

emphasis is on White Box techniques

interfacelocal data structuresboundary conditionsindependent pathserror-handling paths

Component


Test cases

UNIT TESTING — PROCEDURESUNIT TESTING — PROCEDURES

driver and/or stubs must be developed for each unit test

interfacelocal data structuresboundary conditionsindependent pathserror-handling paths

Driver

Stub StubResults

driver: component that calls component to be testedstub: component called by component to be tested

Componentto be tested


INTEGRATION TESTINGINTEGRATION TESTING [9.4.3]

If components all work individually, why more testing?

Big Bang!! Incremental“builds”

Incrementalconstruction

strategy

Regressiontesting

Interaction errors cannot be uncovered by unit testing(e.g., interface misuse, interface misunderstanding, timing errors)

integration approaches:

versus


S2S2

S5S4

S3

S6 S7S6 S7

TOP DOWN INTEGRATION TESTINGTOP DOWN INTEGRATION TESTING

pro –> early testing and error detection of user interface components;can demonstrate a complete function of the system early

con –> cannot do significant low-level processing until late in the testing;need to write and test stubs

usually not appropriate for OO development(except to test operations of classes)

top subsystem is tested with stubs

stubs are replaced one at a time“depth-first” or “breadth-first”

as new subsystems are integrated, some subset of previous tests is re-run (regression testing)

S1

S3

S4 S5


D2

BOTTOM UP INTEGRATION TESTINGBOTTOM UP INTEGRATION TESTING

pro –> interaction faults are more easily found;easier test case design and no need for stubs

con –> user interface components are tested last

appropriate for OO development;test classes using their own test driver

drivers are replaced one ata time “depth-first”

subsystems are groupedinto builds and integrated

S2 S6 S7

S1

S3

S4 S5


pro –> parallel testing activities

con –> need many drivers and stubs

can significantly shortentotal testing time

D2

SANDWICH INTEGRATION TESTINGSANDWICH INTEGRATION TESTING

lower-level subsystems are groupedinto builds and tested with drivers

top-level subsystemsare tested with stubs

S2 S6 S7

S1

S3

S4 S5

S3


INTEGRATION TESTING — CRITICAL SUBSYSTEMSINTEGRATION TESTING — CRITICAL SUBSYSTEMS

Critical subsystems should be tested as early as possible! Critical subsystems should be tested as early as possible!

Critical subsystems are those that:

1. have high risk

2. address several software requirements (i.e., several use cases)

3. have a high level of control

4. are complex or error prone high cyclomatic complexity

5. have specific performance requirements

Regression testing is a must for these subsystems!


SYSTEM TESTINGSYSTEM TESTING [9.4.4]

We need to test the entire system to be sure thesystem functions properly when integrated

We need to test the entire system to be sure thesystem functions properly when integrated

some specific types of system tests:

Functional –> developers verify that all user functions work as specified in the system requirements specification

Performance –> developers verify that the nonfunctional requirements are met

Pilot –> a selected group of end users verifies common functionality in the target environment

Acceptance –> customer verifies usability, functional and nonfunctional requirements against system requirements specification

Installation –> customer verifies usability, functional and nonfunctional requirements in real use


PERFORMANCE TESTINGPERFORMANCE TESTING

stress tests –> verify that the system can continue functioning when confronted with many simultaneous requests How high can we go? Do we fail-soft or collapse?

volume tests –> verify that the system can handle large amounts of data, high complexity algorithms, or high disk fragmentation

security tests –> verify that access protection mechanisms work make penetration cost more than value of entry

timing tests –> verify that the system meets timing constraints usually for real-time and embedded systems

recovery tests –> verify that the system can recover when forced to fail in various ways database recovery is particularly important


PILOT TESTINGPILOT TESTING

Alpha test: a test in a controlled environment so thatdevelopers can observe users

software

Developer site Customer site

customer tests

Beta test: a test in a real environment so that bugs areuncovered from regular usage patterns

Developer site

developerreviews software

Customer site

customertests


ACCEPTANCE TESTINGACCEPTANCE TESTING

the process of ensuring that the software meets the user’s reasonable expectations

Can be very subjective good requirements specification from the start is important!

The method of defect resolution should be negotiated before the transition phase!

acceptance tests (black box) cover classes of tests such as:– functionality – documentation– performance – reliability, etc.

configuration review (audit)– ensures that all elements of the software delivered to the customer

(the software configuration) have been properly developed and documented


EVALUATE TESTSEVALUATE TESTS

We need to– evaluate the results of our testing

– compare the results with the goals outlined in the test plan

– prepare metrics that let the test engineers determine the current quality of the software

How do we know when to stop testing?

We can consider:

– testing completeness: % of test cases run and % of code tested

– reliability: based on testing error rate of previous projects


TESTING ERROR RATETESTING ERROR RATE

Past history can be used to plot expected failure rate.We compare this with actual failure rate for this project.

Testing time

Fai

lure

s pe

r te

st h

our

This project

Expected failure rate

Possible outcomes:• perform additional tests to find more defects• relax the test criteria, if set too high• deliver acceptable parts of the system;

continue testing unacceptable parts

Possible outcomes:• perform additional tests to find more defects• relax the test criteria, if set too high• deliver acceptable parts of the system;

continue testing unacceptable parts


SPECIAL CONSIDERATIONS FOR OO TESTINGSPECIAL CONSIDERATIONS FOR OO TESTING

What to unit test?– unit test has to be at least a class, but object state makes testing

difficult a class must be tested in every state it can ever enter

(i.e., state-based testing)

Encapsulation– encapsulation hides what is inside an object hard to know its state

need to provide a method, for testing only, that reports all of an object’s state

Inheritance and polymorphism– If a subclass overrides methods of an already tested superclass,

what needs to be tested — only the overridden methods? No! All of a subclass’s methods need to be tested again

due to dynamic binding and substitutability


TESTING — FINAL THOUGHTSTESTING — FINAL THOUGHTS

All test are importantAll test are important, but if you need to restrict testing … , but if you need to restrict testing … All test are importantAll test are important, but if you need to restrict testing … , but if you need to restrict testing …

testing a system’s capabilities (functionality) is more important than testing its components– Identify things that will stop users doing their jobs.

testing old capabilities is more important than testing new capabilities– Users expect existing features to keep working!

testing typical situations is more important than testing boundary cases– Normal usage patterns are more important than atypical ones.


DEBUGGINGDEBUGGING [9.3.4]

a consequence of testing, but a separate activity not testing

can be one of the most exasperating parts of development easy to lose focus or follow the wrong path!

time required tocorrect the error

time required todetermine the natureand location of theerror

Debugging islike trying tocure a sickperson.

We see thesymptomsand try tofind thecause.


BE SYSTEMATIC!

DEBUGGING — SYMPTOMS AND CAUSESDEBUGGING — SYMPTOMS AND CAUSES

symptom and cause may begeographically separated

symptom may disappear whenanother problem is fixed

cause may be due to humanerror that is hard to trace

cause may be due to assumptionsthat everyone believes

symptom may be intermittent

cause may be due to a systemor compiler error

symptom

cause

So, what can we do?

pressure to fix bugs often causes new bugs to be introduced


DEBUGGING TECHNIQUESDEBUGGING TECHNIQUES

1. brute force: try to let the computer find the error– run-time traces everywhere

The hope is that somewhere in all this informationwe’ll find the bug!

2. backtracking: start where the problem occurs and read the code backward until the problem is found

OK for small programs.

3. cause elimination: try to create input test data sets that would prove or disprove a particular theory

Difficult, but sometimes your best bet!


DEBUGGING — FINAL THOUGHTSDEBUGGING — FINAL THOUGHTS

debugging tools can help gain more insight into the problem

talk to your colleagues — They can see things you’ve grown too tired to see!

isolate and focus –> Think through the problem—some of the best debugging happens away from the computer!

Be absolutely sure to conduct regression tests when you “fix” the bug!


TESTING SUMMARYTESTING SUMMARY

Plan your tests carefully know what you are trying to test for

Use the right test in the right situation white box, black box, regression

Decide when enough testing has been done have clear criterion for when to stop testing

Be systematic in debugging

09 testing

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