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1 Unit Testing with JUnit CS 3331 Fall 2009 Kent Beck and Eric Gamma. Test Infected: Programmers Love Writing Tests, Java Report, 3(7):37-50, 1998. Available.

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Presentation on theme: "1 Unit Testing with JUnit CS 3331 Fall 2009 Kent Beck and Eric Gamma. Test Infected: Programmers Love Writing Tests, Java Report, 3(7):37-50, 1998. Available."— Presentation transcript:

1 1 Unit Testing with JUnit CS 3331 Fall 2009 Kent Beck and Eric Gamma. Test Infected: Programmers Love Writing Tests, Java Report, 3(7):37-50, Available from:

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

3 3 Testing in General  Testing A way of showing the correctness of software  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 4 What Is Unit Testing?  Definition Testing is the process of showing that a program works for certain inputs. 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, or  A public class along with its helper classes. Unit testing is testing of a unit.

5 5 Question  Do you get more confidence by running more test data?

6 6 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.

7 7 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.

8 8 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.

9 9 Question  How does low coupling help testing?  How does high coupling hurt it?

10 10 Program to Test public final 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; }

11 11 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)); }

12 12 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?

13 13 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

14 14 Testing with JUnit import junit.framework.*; /** A JUnit test class to test the class IMath. */ public class IMathTest extends TestCase { /** Tests isqrt. */ public void testIsqrt() { assertEquals(0, IMath.isqrt(0)); // line 23 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)); }

15 15 Testing with JUnit (Cont.) /** Returns the test suite for this test class. */ public static Test suite() { return new TestSuite(IMathTest.class); } /** Run the tests. */ public static void main(String[] args) { junit.textui.TestRunner.run(suite()); // junit.swingui.TestRunner.run(suite()); }

16 16 Compilation and Output $ javac IMath.java IMathTest.java $ java IMathTest.F Time: 0.02 There was 1 failure: 1)testIsqrt(IMathTest)junit.framework.AssertionFailedError: expected: but was: at IMathTest.testIsqrt(IMathTest.java:23) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMeth... at sun.reflect.Delegating... at IMathTest.main(IMathTest.java:17) FAILURES!!! Tests run: 1, Failures: 1, Errors: 0 Question: Is this better? Why?

17 17 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) {... } }

18 18 Exercise (Cont.) By filling in the following: import junit.framework.*; /** Test ForYou. */ public class ForYouTest extends TestCase { /** 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) {... } }

19 19 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?

20 20 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?

21 21 Basic Usage of JUnit To test a type T: 1. Write a class like: import junit.framework.*; /** A JUnit test class for the class T. */ public class TTest extends TestCase { /** Runs the tests. */ public static void main(String[] args) { junit.textui.TestRunner.run(suite()); } /** Returns the test suite for this test class. */ public static Test suite() { return new TestSuite(TTest.class); } }

22 22 Basic Usage of JUnit (Cont.) 2. Compile T.java and TTest.java $ javac T.java TTest.java 3. Run the JUnit graphical user interface on TTest $ java junit.swingui.TestRunner TTest or Run the text interface (good from makefiles) $ java TTest 4. Look at the failures and errors

23 23 Naming Convention  Test methods start with “test” e.g., testIsqrt, testMin  Test classes end with “Test” e.g., IMathTest, ForYouTest

24 24 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 - Static methods defined in junit.framework.Assert - Variations taking string error messages

25 25 More on JUnit -- Test Fixture  Sharing test data among test methods public class TTest extends TestCase { // other methods here … protected void setUp() throws Exception { // initialize test fixture variables. } protected void tearDown() throws Exception { // uninitialize test fixture variables. } // test fixture variables, i.e., fields shared by several test methods. }

26 26 Example public class PointTest extends TestCase { private Point p; // test fixture variable protected void setUp() { // initializes text fixture variables p = new Point(10, 10); } protected void tearDown() { } // clean up text fixture variables public void testSetX() { // tests SetX p.setX(20); assertEquals(20, p.getX()); } public void testSetY() { // tests SetY p.setY(30); assertEquals(30, p.getY()); } // template and other test methods here… }

27 27 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.

28 28 Example public class AllTestSuite extends TestCase { /** Returns the test suite for this test class. */ public static Test suite() { TestSuite suite = new TestSuite() { public String toString() { return "Test suite for Project T"; } }; suite.addTestSuite(T1Test.class); suite.addTestSuite(T2Test.class); … suite.addTestSuite(TnTest.class); return suite; } // the rest of methods as before … }

29 29 More on JUnit?  Refer to  JUnit APIs available from the course Web page


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