Testing with JUnit 1

Transcription

1 Testing with JUnit 1

2 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

3 Origins and current status 3

4 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

5 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

6 A simple example 6

7 Stack: A poor implementation 7 7

8 But let s test it anyway - detail follows 8 8

9 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

10 A number of tests may appear in the class Each called testsomething Each prefixed (no quotes, no ; ) This is a JUnit 4 feature, use JUnit

11 Demo Explore (and run) the tests 11 11

12 More detail Seems reasonable... But it assumes we have initialised s, our stack implementation 12 12

13 Pre test-initialisation Use tag for the method setup setup is then run before each test 13 13

14 What if we didn t have a pre-test setup? Eg

15 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

16 Summary: To provide test independence We need to set up tests to run tags a setup method to run immediately before each test 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 documentation 16 16

17 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

18 Test order example 18 18

19 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

20 More about assertions, good style 20

21 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

22 Old and new styles Note the extra (first) argument to assertthat do we need it? Demo both tests Note different output 22 22

23 Some matchers equalto(...) is(...) not(...) note not(equalto(...)) etc nullvalue(...), notnullvalue(...) instanceof(...) hasiteminarray(...) 23 23

24 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 messages Expected: (a string containing "color" or a string containing "colour") Got: "Utter, complete and total darkness"" 24 24

25 Find out more for yourselves Read this Comprehensive example of assertions and matchers from JUnit and Hamcrest Follow these up if you want/need to Timeouts for tests Fixtures for tests in a class for all tests in a class) Running from the command line

26 Finally, this may help you 26

27 Ignoring a test on the line 27 27

28 Test cycle: Red, green, refactor RED GREEN