1 Unit Testing with JUnit CS 3331 JUnit website at Kent Beck and Eric Gamma. Test Infected: Programmers Love Writing Tests, Java Report, 3(7):37-50, Available from:

2 Unit Testing  Introduction  Conventional approach  Unit testing with JUnit  More on JUnit

3 Introduction  Testing A process of showing that a program works for certain inputs  Phases Unit testing  To test each module (unit, or component) independently  Mostly done by developers of the modules Integration and system testing  To test the system as a whole  Often done by separate testing or QA team Acceptance testing  To validate system functions for (and by) customers or user

4 What Is Unit Testing?  Testing focusing on the smallest units of code, such as Functions, procedures, subroutines, subprograms Methods, classes  Component tested in isolation from the rest of the system and in a controlled environment: Uses appropriately chosen input data Uses component-level design description as guide  Unit testing is testing of a unit.  Often the target of testing frameworks such as JUnit

5 Unit in Java?  A unit is a module or a small set of modules.  In Java, a unit is a class or interface, or a set of them, e.g., An interface and 3 classes that implement it A public class along with its helper classes.

6 Question  Do you get more confidence by running more test data?

7 Why Unit Testing?  Code isn’t right if it’s not tested.  Practical Most programmers rely on testing, e.g., Microsoft has 1 tester per developer. You could get work as a tester.  Divide-and-conquer approach Split system into units. Debug unit individually. Narrow down places where bugs can be. Don’t want to chase down bugs in other units.

8 Why Unit Testing? (Cont.)  Support regression testing So can make changes to lots of code and know if you broke something. Can make big changes with confidence.

9 How to Do Unit Testing  Build systems in layers Starts with classes that don’t depend on others. Continue testing building on already tested classes.  Benefits Avoid having to write (test) stubs. When testing a module, ones it depends on are reliable.

10 Question  How does low coupling help testing?  How does high coupling hurt it?

11 Program to Test public class IMath { /** Returns an integer approximation to the square root of x. */ public static int isqrt(int x) { int guess = 1; while (guess * guess < x) { guess++; } return guess; }

12 Conventional Testing /** A class to test the class IMath. */ public class IMathTestNoJUnit { /** Runs the tests. */ public static void main(String[] args) { printTestResult(0); printTestResult(1); printTestResult(2); printTestResult(3); printTestResult(4); printTestResult(7); printTestResult(9); printTestResult(100); } private static void printTestResult(int arg) { System.out.print(“isqrt(“ + arg + “) ==> “); System.out.println(IMath.isqrt(arg)); }

13 Conventional Test Output Isqrt(0) ==> 1 Isqrt(1) ==> 1 Isqrt(2) ==> 2 Isqrt(3) ==> 2 Isqrt(4) ==> 2 Isqrt(7) ==> 3 Isqrt(9) ==> 3 Isqrt(100) ==> 10  What does this say about the code? Is it right?  What’s the problem with this kind of test output?

14 Solution?  Automatic verification by testing program Can write such a test program by yourself, or Use a testing tool such as JUnit  JUnit A simple, flexible, easy-to-use, open-source, and practical unit testing framework for Java Can deal with a large and extensive set of test cases Refer to

15 Testing with JUnit import org.junit.Test; import static org.junit.Assert.*; /** A JUnit test class to test the class IMath. */ public class IMathTest { /** Test isqrt. public void testIsqrt() { assertEquals(0, IMath.isqrt(0)); // line 13 assertEquals(1, IMath.isqrt(1)); assertEquals(1, IMath.isqrt(2)); assertEquals(1, IMath.isqrt(3)); assertEquals(2, IMath.isqrt(4)); assertEquals(2, IMath.isqrt(7)); assertEquals(3, IMath.isqrt(9)); assertEquals(10, IMath.isqrt(100)); }

16 Testing with JUnit (Cont.) /** Run the tests. */ public static void main(String[] args) { org.junit.runner.JUnitCore.main("IMathTest"); }

17 Compilation and Output $ javac IMath.java IMathTest.java $ java IMathTest JUnit version 4.10.E Time: There was 1 failure: 1) testIsqrt(IMathTest) java.lang.AssertionError: expected: but was: at org.junit.Assert.fail(Assert.java:93) … at IMathTest.main(IMathTest.java:13) FAILURES!!! Tests run: 1, Failures: 1 Question: Is this better? If so, why?

18 Exercise  Write a JUnit test class for testing public class ForYou { /** Return the minimum of x and y. */ public static int min(int x, int y) {... } }

19 Exercise (Cont.) public class ForYouTest { /** Test min. public void testMin() { } // the rest as before … } public class ForYou { /** Return the minimum of x and y. */ public static int min(int x, int y) {... } } In Eclipse, - Select a source code folder - Right click (pop-up menu) - Select New > Other… > JUnit > Junit Test Case

20 Some Terminology  Definition A test data (or case) for a method M is a pair of (o, args), where  o is not null and M can be sent to o,  args is a tuple of arguments that can be passed to M. A test data, (o, args), for M succeeds iff o.M(args) behaves as expected. A test data, (o, args), for M fails iff it does not behave as expected.  Question Why should o not be null? If M has a bug that is revealed by a test data, does that test data for M succeeds or fails?

21 Parts of Test Code  Definition The test fixture is the set of variables used in testing. The test driver is the class that runs the tests. The test oracle for a test data is the code that decides success or failure for that test data.  Question What in the code we saw so far was the test driver, and the oracle? What difference is there between JUnit testing and non-JUnit testing in what we saw before?

22 Basic Usage of JUnit To test a type T: 1. Write a class like: import org.junit.*; import static org.junit.Assert.*; /** A JUnit test class for the class T. */ public class TTest { /** Runs the tests. */ public static void main(String[] args) { org.junit.runner.JUnitCore.main(“T") public void testM1() { … } }

23 Basic Usage of JUnit (Cont.) 2. Compile T.java and TTest.java, e.g., $ javac T.java TTest.java 3. Run the JUnit in IDE such as Eclipse, e.g., Select Run As > JUnit Test or Run the text interface $ java TTest 4. Look at the failures and errors

24 Naming Convention  Test methods start with “test” e.g., testIsqrt, testMin  Test classes end with “Test” e.g., IMathTest, ForYouTest

25 Assertion Methods Method Description assertEquals(a,b)Test if a is equal to b assertFalse(a)Test if a is false assertNotSame(a, b)Test if a and b do not refer to the identical object assertNull(a)Test if a is null assertSame(a,b)Test if a and b refer to the identical object assertTrue(a)Test if a is true fail()Fail a test - Static methods defined in org.junit.Assert - Variations taking string error messages

26 Testing Exceptions  Use optional parameter “expected” annotation  Q: Without using public void indexingEmptyList() { new ArrayList ().get(0); }

27 More on JUnit -- Test Fixture  Sharing test data among test methods public class TTest { // test fixture variables, i.e., fields shared by several test public void setUp() throws Exception { // initialize test fixture variables. public void tearDown() throws Exception { // uninitialize test fixture variables. } // test methods … } Also refer annotations.

28 Example public class PointTest { private Point public void setUp() { p = new Point(10, 10); public void testSetX() { p.setX(20); assertEquals(20, p.getX()); assertEquals(10, p.getY()); public void testSetY() { p.setY(30); assertEquals(30, p.getY()); assertEquals(10, p.getX()); } Q: What is omitted and p is initialized to new Point(10,10)?

29 More on JUnit -- Test Suite  Definition A test suite is a set of test methods and other test suites.  Test Suite Organize tests into a larger test set. Help with automation of testing.

30 Example import org.junit.runner.RunWith; PlaceTest.class, BattleshipTest.class, BattleFieldTest.class }) public class AllTests { } In Eclipse, - Select a source code folder - Right click (pop-up menu) - Select New > Other … > JUnit > Junit Test Suite

31 More on JUnit?  Refer to