Unit Testing 0

8/8/2019 Unit Testing 0

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Software Construction

Unit Testing

Christoph Denzler / Martin KroppUniversity of Applied Sciences Northwestern SwitzerlandInstitute for Mobile and Distributed Systems


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Agenda

Introduction into Testing

Unit TestingTesting with JUnit

UnitTesting (Part1), FS2010 IMVS, Ch. Denzler/M. Kropp 3


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The Why, The What, The How

It has to do with quality!

Your software has to meet customerre uirements

functional and non-functional requirements

How do you ensure that your software doeswhat it should?



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It has to do with safety!

You often have to change your existing codebecause of new re uirements, im rovements,and bug fixes

How do you ensure, that your changed softwarestill does what it did before?



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It has to do with sustainability!

You still have to fix bugs

How do you ensure, that a fixed bug nevershows up again? (or you notice it immediately,at least)



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What is Testing?

Testing is the process of evaluating a particular

product to determine if it meets the customersrequirements.

That means1. There must be well specified requirements to

test against (expected results)2. Testing is comparing actual results to expected

results



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What is Testing?

The deviation of an actual result from an

expected result, is called a defectTesting can only show the presence of a defectbut not the absence of defects



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The First Bug

Grace Hoppers bug (moth stuck in a relay on

an early machine)



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Some Famous Software Failures

1991: The Patriot Missile failure , in Dharan, Saudi Arabia, on February 25, 1991which resulted in 28 deaths, is ultimately attributable to poor handling of roundingerrors.1991: The sinking of the Sleipner A offshore platform in Gandsfjorden nearStavanger, Norway, on August 23, 1991, resulted in a loss of nearly one billiondollars. It was found to be the result of inaccurate finite element analysis.1996: The explosion of the Ariane 5 rocket just after lift-off on its maiden voyageoff French Guiana, on June 4, 1996, was ultimately the consequence of a simpleoverflow.1999: NASAs Mars lander , September 1999, crashed due to a units integrationfaultover $50 million US !2005: Arbeitslosengeld II = ALG-II in Germany:writing 9 digit bank codes left-aligned in 10 digit fields leads to adding a zero at the end and wrong bank codes.2010: Year 2010 bug on German bankcards (Jan 4 2010): It showed up to be asoftware defect due to incorrect year handling.

More on http://www5.in.tum.de/~huckle/bugse.html



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You can do this manually

Writing test specifications and protocolsOr (much better) automated

Let the system do it for you (at least part of it)



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Testing Dimensions

Level

system

integration

component


Accessibility

Target

unit

white box black box stress

performance

reliability

usability

robustness

functionality


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The Testing Process

Test case

Test data

Testresults

Testreport


cases

data

tests

results to test data


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Unit Testing

Unit Testing is done

on each modulein isolationto verify the units behavior


Unit test willestablish some kind of artificial environmentinvoke routines in the module under test

check the results against expected values


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Using Test Frameworks

Provides following capabilities

test specificationtest implementationstandard way to specify setup and cleanup


method for selecting individual tests or all availabletestsmeans of analyzing output for expected (orunexpected) resultsstandardized form of failure reporting

=> Use JUnit for Java Unit Testing


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JUnit 4 Examplepackage unittesting;import java.util.NoSuchElementException;

public class IntArray {

private int[] array;

public IntArray(int[] values) { array = values; }

public int findLargest() throws NoSuchElementException {


int max = Integer.MAX_VALUE;if (array.length == 0) { throw new NoSuchElementException(); }for (int num : array) {

if (num > max) {max = num;

}}return max;

}}


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JUnit4

Uses annotations, static import

Setup, Cleanup@Before, @After@BeforeClass, @AfterClass


@Test@Test(expected=MovieMgmtException.class)@Ignore

CheckingAssert (use "static import")


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Using JUnit Asserts

Use Asserts byusing the prefixed syntaxAssert.assertEquals()

importing statically the Assert classimport static org.unit.Assert.assertEquals


assertEquals()assertEquals([String message], expected, actual)assertEquals([String message], expected, actual,

tolerance)

assertNull(), assertNotNull(), assertSame(), assertNotSame(),assertTrue(), assertFalse(), fail()


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Organizing Your Test

Separate tests from production code

myProject/trunk/src/prod/src/test // as under prod/src/test/data // for test data

Put it into the same packages


log takes all output

myProject/trunk/src/prod/ch.fhnw.edu.rental.model/src/test/ch.fhnw.edu.rental.model


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Reflections on Unit Testing

Coding with ConfidenceWhat is Unit Testing?Why should I bother with Unit Testing?What do I want to accomplish?

Does it do what I want?Does it do what I want all the time?Can I depend on it?Does it document my intent?


ow o o n es ngBad Excuses for not Unit Testing

It takes too much time to write the testsIt takes too long to run the testsIt's not my job to test my codeI don't really know how the code is supposed to behave so I can't test itBut it compiles

I'm being paid to write code, not to write testsI feel guilty about putting testers and QA staff out of workMy company won't let me run unit tests on the live system

from "Pragmatic Unit Testing"


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And Finally

Some pragmatic tips

Test Early. Test Often. Test Automatically.


Coding Ain't Done 'Til All the Tests Run.Tip 63 (The Pragmatic Programmer)

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