Unit Testing with JUnit CS 3331 JUnit website at http://www.junit.org Kent Beck and Eric Gamma. Test Infected: Programmers Love Writing Tests, Java Report, 3(7):37-50, 1998. Available from: http://junit.sourceforge.net/doc/testinfected/testing.htm

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

Introduction Testing Phases 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

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

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.

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

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.

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.

How to Do Unit Testing Build systems in layers Benefits 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.

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

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;

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));

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?

Solution? Automatic verification by testing program JUnit 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 www.junit.org

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. */ @Test 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)); }

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

Compilation and Output $ javac IMath.java IMathTest.java $ java IMathTest JUnit version 4.10 .E Time: 0.015 There was 1 failure: 1) testIsqrt(IMathTest) java.lang.AssertionError: expected:<0> but was:<1> 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?

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) { ... } }

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

Some Terminology Definition Question 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?

Parts of Test Code Definition Question 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?

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") } <test methods go here, e.g.,> @Test public void testM1() { … }

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

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

Assertion Methods - Static methods defined in org.junit.Assert 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

Testing Exceptions Use optional parameter “expected” of @Test annotation Q: Without using “expected”? @Test(expected=IndexOutOfBOundsException.class) public void indexingEmptyList() { new ArrayList<Object>().get(0); }

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

Example private Point p; @Before public void setUp() { public class PointTest { private Point p; @Before public void setUp() { p = new Point(10, 10); } @Test 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 if @Before is omitted and p is initialized to new Point(10,10)?

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.

Example import org.junit.runner.RunWith; import org.junit.runners.Suite; @RunWith(Suite.class) @Suite.SuiteClasses({ 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

More on JUnit? Refer to www.junit.org