Testing Fundamentals - York University · Testing Fundamentals Need for, Black box, White box,...

Testing Fundamentals

Need for, Black box, White box, Minimal output

Need for Testing

n  Software systems are inherently complexn  Large systems 1 to 3 errors per 100 lines of code (LOC)

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Need for Testing

n  Extensive verification and validiation is required to build quality software

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Need for Testing

n  Extensive verification and validiation is required to build quality softwaren  Verification

n  Does the software meet its specifications

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Need for Testing

n  Does the software meet its specificationsn  Validation

n  Does the software meet its requirements

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Need for Testing

n  Does the software meet its specificationsn  Validation

n  Does the software meet its requirements

n  Testing is used to determine whether there are faults in a software system

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Need for Testing

n  The process of testing is to find the minimum number of test cases that can produce the maximum number of failures to achieve a desired level of confidence

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Need for Testing

n  Cost of validation should not be under estimated

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Need for Testing

n  Cost of validation should not be under estimated

n  The cost of testing is extremely highn  Anything that we can do to reduce it is worthwhile

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Testing Not Enough

n  Exhaustive testing is not usually possible

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Testing Not Enough

n  Exhaustive testing is not usually possibleTesting can determine the presence of faults, never their absence

Dikstra

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Testing Not Enough

n  Exhaustive testing is not usually possibleTesting can determine the presence of faults, never their absence

Dikstra

n  Test to give us a high level of confidence

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Test Strategy

n  Identify test criterian  What are the goals for comparing the system against its

specificationn  Reliability, completeness, robustness

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Test Strategy

n  Identify test criterian  What are the goals for comparing the system against its specification

n  Reliability, completeness, robustness

n  Identify target components for testingn  In an OO system the classes and class hierarchies

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Test Strategy

n  Generate test casesn  Produce test cases that can identify faults in an

implementation

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Test Strategy

n  Generate test casesn  Produce test cases that can identify faults in an implementation

n  Execute test cases against target components

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Test Strategy

n  Generate test casesn  Produce test cases that can identify faults in an implementation

n  Execute test cases againsr target components

n  Evaluationn  If expected outputs are not produced, a bug report is issued

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Test Plans

n  Specify a set of test input

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Test Plans

n  For each input give the expected output

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Test Plans

n  Run the program and document the actual output

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Test Plans

n  Run the program and document the actual output

n  Example – square root programn  Input: 4.0n  Expected Output: 2.0n  Actual Output: 1.99999 looks all right

n  Input: -4n  Expected Output: Invalid inputn  Actual Output: 1.99999 Uh oh! problem here

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Black Box Testing – Data Coverage

n  Testing based on input and output alonen  Do not consider underlying implementation

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n  Test cases are generated from the specificationn  Pre and post conditions

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n  Specific kinds of black box testingn  Random testing

n  Generate random inputsn  Easy to generate casesn  good at detecting failuesn  Must be able to easily generate expected output

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n  Specific kinds of black box testingn  Random testing

n  Generate random inputsn  Easy to generate casesn  good at detecting failuesn  Must be able to easily generate expected output

n  Partition testingn  See next slides

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Partition Testing

n  Cannot try all possible inputs

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Partition Testing

n  Cannot try all possible inputsn  Partition input into equivalence classes

n  Every value in a class should behave similarly

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Partition Testing

n  Test casesn  just before boundaryn  just after a boundaryn  on a boundaryn  one from the middle of an equivalence class

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Partition Testing

n  Test casesn  just before boundaryn  just after a boundaryn  on a boundaryn  one from the middle of an equivalence class

n  Loopsn  Zero times through the bodyn  Once through the bodyn  Many times through the body

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Partition Testing examples

n  Example 1 – Absolute value – 2 equivalence classes

n  Values below zero and values above zero

n  5 test cases: large negative, -1, 0, +1, large positive

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n  Example 2 – Tax rates – 3 equivalence classesn  0 .. $29,000 at 17%

n  29,001 .. 35,000 at 26%

n  35,001 ... at 29%

n  13 Test cases 0 1 15,000 28,999 29,000 29,001 29,002 30,000 34,999 35,000 35,001 35,002 50,000

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n  Example 3 – Insert into a sorted list -- max 20 elements

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n  About 25 test cases

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n  About 25 test casesn  Boundary conditions on the list

n  empty boundary – length 0, 1, 2n  full boundary – length 19, 20 , 21n  middle of range – length 10

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n  Boundary conditions on insertingn  just before & after first list elementn  just before & after last list elementn  into the middle of the list

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n  Boundary conditions on insertingn  just before & after first list elementn  just before & after last list elementn  into the middle of the list

n  Suppose an error occurs when adding to the upper end of a full listn  Devise additional test cases to test hypothesis as to why

the error occurs

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White Box Testing

n  Use internal properties of the system as test case generation criteria

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White Box Testing

n  Generate cases based onn  Statement blocksn  Paths

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White Box Testing

n  Identify unintentionaln  Infinite loopsn  Illegal pathsn  Unreachable program text (dead code)

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White Box Testing

n  Identify unintentionaln  Infinite loopsn  Illegal pathsn  Unreachable program text (dead code)

n  Need test cases for exceptions and interrupts

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Statement Coverage

n  Make sure every statement in the program is executed at least once

n  Examplen  if a < b then c = a+b ; d = a*b /* 1 */

else c = a*b ; d = a+b /* 2 */if c < d then x = a+c ; y = b+d /* 3 */ else x = a*c ; y = b*d /* 4 */

n  Statement coverage – can do with 2 testsn  Execute 1 & 3 with a < b & a+b < a*b

n  a = 2 ; b = 5n  Execute 2 & 4 with a >= b & a*b >= a+b

n  a = 5 ; b = 2

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Statement Coverage

n  Loops – only 1 test requiredn  Execute body at least oncen  If there are choices in the body, need to execute body with

enough tests to execute the statements in the body, analogous to example 1.

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Top Down Testing

n  Test upper levels of program first

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Top Down Testing

n  Use stubs for lower levels

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Top Down Testing

n  Use stubs for lower levelsn  Stubs are dummy procedures that have "empty"

implementations – do nothing

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Top Down Testing

implementations – do nothingn  For functions return a constant value

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Top Down Testing

implementations – do nothingn  For functions return a constant value

n  Test calling sequences for procedures and simple cases for upper levels.

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Bottom Up Testing

n  Use test drivers

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Bottom Up Testing

n  Use test driversn  Have complete implementation of subprograms

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Bottom Up Testing

n  Use test driversn  Have complete implementation of subprogramsn  Create a special main program to call the subprograms with

a sequence of test cases

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Bottom Up Testing

a sequence of test casesn  Can be interactive, semi-interactive, or non-interactive

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Bottom Up Testing

a sequence of test casesn  Can be interactive, semi-interactive, or non-interactive

n  See minimal output test program slides

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Mixed Top & Bottom Testing

n  Use scaffolding

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n  Use scaffoldingn  Have some stubs

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n  Use scaffoldingn  Have some stubsn  Have some special test drivers

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n  Use scaffoldingn  Have some stubsn  Have some special test driversn  Like the scaffolding around a building while it is being built

or repaired

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n  Use scaffoldingn  Have some stubsn  Have some special test driversn  Like the scaffolding around a building while it is being built

or repairedn  Not a part of the final product but necessary to complete

the task

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Regressive Testing

n  Rerun all previous tests whenever a change is made

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Regressive Testing

n  Rerun all previous tests whenever a change is maden  Changes can impact previously working programs

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Regressive Testing

n  Rerun all previous tests whenever a change is maden  Changes can impact previously working programsn  So retest everything

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Regressive Testing

n  Rerun all previous tests whenever a change is maden  Changes can impact previously working programsn  So retest everythingn  Must also test the changes

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Minimal Output Testing

n  Reading and comparing expected with actual output is tedious and error prone

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n  Task should be automated – especially for regressive testing

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n  Build the expected output into the test driver and compare with the actual output

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n  Report only if expected ≠ actualn  Output states which test failed, the expected and the actual

outputs

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n  Report only if expected ≠ actualn  Output states which test failed, the expected and the actual

outputs

n  Successful test runs only output the messagen  Tests passed

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Minimal Output Testing – 2

n  Example checking a stack implementation   Stack list = new Stack(); verifyEmpty("1", list);

list.add("a"); verifyL1("2", list, "[ a ]");list.remove(); verifyEmpty("3", list);list.add("a");list.add("b"); verifyL2("4", list, "[ b , a ]");

  if (list.contains("c")) println("5 shouldn't contain c");if (!list.contains("a")) println("6 should contain a");if (!list.contains("b")) println("7 should contain b");

  list.add("c"); verifyL3("8", list, "[ c , b , a ]");list.remove(); verifyL2("9", list, "[ b , a ]");list.remove(); verifyL1("10", list, "[ a ]");list.remove(); verifyEmpty("11", list);

n  Verify routines do the appropriate test and output messages

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Assertions

n  Running programs with a life jacket

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Assertions

n  Running programs with a life jacketn  Assertions are tested whenever the program is executed,

unlike testing which is done off-line

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Assertions

n  Running programs with a life jacketn  Assertions are tested whenever the program is executed, unlike

testing which is done off-line

n  Assertions can be put into programs using if...then statementsn  Some languages such as Eiffel have them built inn  C has the assert macro

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Assertions

n  Running programs with a life jacketn  Assertions are tested whenever the program is executed, unlike

testing which is done off-line

n  Assertions can be put into programs using if...then statementsn  Some languages such as Eiffel have them built inn  C has the assert macro

n  The condition compares expected with actual values and executes an exception if the assertion fails

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Inspections & Walkthroughs

n  Manual or computer aided comparisons of software development products

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n  Manual or computer aided comparisons of software development productsn  specifications, program text, analysis documents

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n  Documents are paraphrased by the authors

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n  Walkthroughs are done by going through the execution paths of a program, comparing its outputs with those of the paraphrased documents

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n  Walkthrough teamn  Usually 4-6 people

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n  Walkthrough teamn  Usually 4-6 peoplen  Elicit questions, facilitate discussion

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n  Walkthrough teamn  Usually 4-6 peoplen  Elicit questions, facilitate discussionn  Interactive process

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n  Walkthrough teamn  Usually 4-6 peoplen  Elicit questions, facilitate discussionn  Interactive processn  Not done to evaluate people

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n  Walkthrough teamn  Usually 4-6 peoplen  Elicit questions, facilitate discussionn  Interactive processn  Not done to evaluate people

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n  Psychological side effects

n  If a walkthrough is going to be performed, developers frequently write easy to read program text

n  This clarity can help make future maintenance easier

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OO Testing

n  Using OO technology can have effects on three kinds of testingn  Intra featuren  Inter feature testingn  Testing class hierarchies

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OO Testing

n  Intra feature testingn  Features can be tested much as procedures & functions are

tested in imperative languages

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OO Testing

n  Intra feature testingn  Features can be tested much as procedures & functions are tested

in imperative languages

n  Inter feature testingn  Test an entire class against an abstract data type

(specification)n  Some inter-feature testing methods specify correct

sequences of feature calls, and use contracts to derive test cases

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Testing Class Hierarchies

n  May have re-test inherited features

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n  For testing a hierarchy it is usually best to test from the top downn  Start with base classesn  Test each feature in isolationn  Then test feature interactions

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n  For testing a hierarchy it is usually best to test from the top downn  Start with base classesn  Test each feature in isolationn  Then test feature interactions

n  Build test historiesn  Associate test cases with featuresn  History can be inherited with the class, allowing for reuse of

test cases

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Testing Classes

n  Consider the class as the basic unit

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Testing Classes

n  Like unit (module) testingn  Usually tested in isolationn  Surround class with stubs and drivers

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Testing Classes

n  Exercise each feature in turnn  Create test cases for each feature

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Testing Classes

n  Often a test driver is createdn  Simple menu that can be used to exercise each feature with

inputs from a test file

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Testing Classes

n  Often a test driver is createdn  Simple menu that can be used to exercise each feature with

inputs from a test file

n  Need to recompile when switching drivers

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Integration Testing

n  Testing with all the components assembled

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Integration Testing

n  Focuses on testing the interfaces between components

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Integration Testing

n  Usually want to do this in a piece by piece fashion

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Integration Testing

n  Usually want to do this in a piece by piece fashionn  Avoid a big bang test

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Integration Testing

n  Usually want to do this in a piece by piece fashionn  Avoid a big bang testn  Incremental testing and incremental integration is

preferable

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Integration Testing

n  Usually want to do this in a piece by piece fashionn  Avoid a big bang testn  Incremental testing and incremental integration is

preferablen  Integrate after unit testing a component

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Integration Testing

n  Usually want to do this in a piece by piece fashionn  Avoid a big bang testn  Incremental testing and incremental integration is preferable

n  Integrate after unit testing a component

n  Bottom up and top down approaches may be used

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