Testing with JUnit

1

What are we doing here?

• Learning the mechanics of how to write tests in Java using JUnit • Without considering issues like coverage

• Using JUnit is sometimes called unit testing • Unit testing is great for testing the functionality of

classes • Unit testing is used in Test Driven Development

(TDD)

2

Origins and current status

3

Origins

• Kent Beck developed the first automated test tool for in mid-90’s • XUnit, developed for Smalltalk

• Beck and Gamma developed JUnit on a flight from Zurich to Washington DC • Martin Fowler: “Never in the field of software development was so much owed by so many to so few lines of code.”

4

4

Currently

• Junit is now the standard tool for Test-Driven Development in Java

• Junit test generators now part of many Java IDEs (Eclipse, JBuilder, Intellij)

• Language similar to JUnit have been developed for other languages (Perl, C++, Python, Visual Basic, C#, …)

5

5

A simple example

6

Stack: A poor implementation

7

7

But let’s test it anyway - detail follows

8

8

One class for the tests

• Call it SomethingTest • Something = the class you are testing

• Put the test subject in the class as an instance variable

9

9

A number of tests may appear in the class• Each called testSomething • Each prefixed with ‘@Test’ (no quotes, no ‘;’)

• This is a JUnit 4 feature, use JUnit 4

10

10

Demo

• Explore (and run) the tests

11

11

More detail

• Seems reasonable... !!!!

• But it assumes we have initialised ‘s’ , our stack implementation

12

12

Pre test-initialisation

• Use the ‘@Before’ tag for the method ‘setUp’ • setUp is then run before each test !!!!

13

13

What if we didn’t have a pre-test setup?• Eg....

14

14

What’s the problem?• JUnit’s test runner can run all the tests in our test

class, assume we run these tests in this order..

15

15

Summary: To provide test independence• We need to set up tests to run independently • ‘@Before’ tags a setup method to

run immediately before each test • Similarly ‘@After’ tags a teardown method to run

after each test runs • Do we need a teardown method for this example? !

• Default behaviour for independent tests • Tests run in a random order = good practice • You can change this, see the next slides and

the JUnit documentation16

16

Test order

• Not determined, eg Java 1.7 executes tests in a random order

• Annotate the class if you want a particular order !!!!

• Ordering • JVM, DEFAULT, NAME_ASCENDING • Nothing for ‘in-class declaration’ order

17

17

Test order example

18

18

On screen demo

• Let’s play around with the tests.... • Wow, with a test suite we can refactor our

implementation safely • I did that to provide a better stack implementation

19

19

More about assertions, good style

20

assertThat and matcher statements

• Using ‘assertThat’ improves readability • assert that x is 3 • assertThat( x, is(3) ); • assertThat(<value>, is(<expected value>)) • assertThat(<value>, <matcher statement>)

• Matcher statements • is(....), lessThan(....), sameInstance(....) • Matchers are defined in

• org.hamcrest.CoreMatchers • Only two non-deprecated matchers in

org.junit.matchers.JUnitMatchers 21

21

Old and new styles

!!!!!!!

• Note the extra (first) argument to ‘assertThat’ • do we need it?

• Demo both tests • Note different output 22

22

Some matchers

• equalTo(....) • is(....) • not(....) note not(equalTo(....)) etc • nullValue(....), notNullValue(....) • instanceOf(....) • hasItemInArray(....)

23

23

Combining matchers

• There are ways of writing assertions to perform logical operations

• Lets test that a variable ‘responseString’ contains either ‘colour’ or ‘color’assertThat( responseString, anyOf( containsString("color"), containsString("colour") ) );

!• This kind of construct gives great failure messagesExpected: (a string containing "color" or a string containing "colour") Got: "Utter, complete and total darkness""

24

24

Find out more for yourselves

• Read this • https://github.com/junit-team/junit/wiki/Assertions

• Comprehensive example of assertions and matchers from JUnit and Hamcrest

• Follow these up if you want/need to • Timeouts for tests

https://github.com/junit-team/junit/wiki/Timeout-for-tests • Fixtures for tests in a class

(an ‘@Before’ for all tests in a class)https://github.com/junit-team/junit/wiki/Timeout-for-tests

• Running from the command line https://github.com/junit-team/junit/wiki/Test-runners

25

25

Finally, this may help you

26

Ignoring a test

• Put @Ignore on the line above @Test

27

27

Test cycle: Red, green, refactor

28

GREENRED

https://octoberclub.wordpress.com/2011/10/04/tidying-up-technical-debt-using-tdd/

28