Unit Testing with JUnit4

1. Unit Testing with JUnit 4
Ravikiran Janardhana
COMP 401: Foundations of Programming
UNC – Chapel Hill
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2. Source: http://www.leonardscomic.com/comic/68/unit-testing/ 2

3. Testing
Testing is the activity of finding out whether a
piece of code (method / program) produces
the intended behavior.
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4. 4

5. Testing phases
• Unit Testing on individual units of source
code (mostly methods)
• Integration Testing on groups of individual
software modules
• System testing on a complete end-to-end
system
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6. Example: Assignment 2
• PolygonImpl
– Create a polygon with „n‟ points
– Compute area
– Compute centroid
• How to test if the functionality implemented
is correct ? Use JUnit
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7. Installing JUnit
• Eclipse users – You are in good shape. JUnit
is already installed for you  !
• Caveat: Make sure you are using JUnit4
instead of JUnit3, update if required
• Ubuntu - sudo apt-get install junit4
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8. JUnit Demo Source Code
• JUnit Demo Source Code
– Online (tiny url):
http://bit.ly/XG97oO
– Online (source) :
https://docs.google.com/a/cs.unc.edu/file/d/0B3luEI_yhbZWMm
RpQTlHS2pGNE0/edit?usp=sharing
– Delete/Rename PolygonImplTest.java if you want to code it
during this session
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9. Creating a new JUnit TestCase
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10. Creating a new JUnit TestCase
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11. Creating a new JUnit TestCase
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12. Testing in JUnit
• Tests are written as “public void testX()”
methods (good practice).
• Use @Test annotation to mark a method
as a test case. (compulsory)
• Annotations provide data about a program
that is not part of the program itself.
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13. Annotations
• @Test – mark a method as test
• @BeforeClass – run once before all tests
• @AfterClass – run once after all tests
• @Before – called before every testX()
• @After – called after every testX()
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14. 14

15. Part I : Initialize
package demo;
import static org.junit.Assert.assertEquals;
import org.junit.After;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;
public class PolygonImplTest{
private PolygonImpl p;
// One Time Setup
@BeforeClass
public void runOnceBeforeAllTests(){
}
// Tear down after all tests
@AfterClass
public void runAfterAllTests(){
}
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16. Part I : Initialize (Setup)
// Creates test environment (fixture).
// Called before every testX() method.
@Before
public void setUp() throws Exception {
Point a = new Point(-1, -2);
Point b = new Point(-2.5, -3.5);
Point c = new Point(-3.1, -1.4);
Point d = new Point(-2, 1.3);
Point e = new Point(1, 1);
Point f = new Point(2, 3);
Point g = new Point(3, 0.5);
Point h = new Point(5, 2.5);
Point i = new Point(4, -2);
Point j = new Point(1.5, -1.5);
Point[] poly_points = new Point[] {a, b, c, d, e, f, g, h, i, j};
this.p = new PolygonImpl(poly_points)
} 16

17. Part I : Initialize (Tear Down)
// Releases test environment (fixture).
// Called after every testX() method.
@After
public void tearDown() throws Exception {
p = null;
}
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18. Part II: Write Test Cases
• Helper methods to test:
fail(msg) – triggers a failure named msg
assertTrue(msg, b) – triggers a failure, when condition b is false
assertEquals(msg, v1, v2) – triggers a failure, when v1 == v2 is false ✓
assertEquals(msg, v1, v2, eps) – triggers a failure, if abs(v1 – v2) > eps ✓
assertNull(msg, object) – triggers a failure, when object is not null
assertNonNull(msg, object) – triggers a failure, when object is null
The parameter msg is optional 18

19. Test getArea() and getCentroid()
@Test
public void testPolygonArea() {
assertEquals("P1: polygon area is wrong", p.getArea(), 24.24, 0.01);
}
@Test
public void testPolygonCentroid() {
Point centroid = p.getCentroid();
assertEquals("P2: centroid (x) is wrong", centroid.getX(), 0.7646, 0.01);
assertEquals("P2: centroid (y) is wrong", centroid.getY(), -0.3067, 0.01);
//The below assertion will print an AssertionFailedError, can you tell me
why ?
//But it may also pass with some modification to Point class
assertEquals("P2: centroid is wrong", p.getCentroid(), new Point(0.7646,
-0.3067));
}
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20. Junit Test Result
Source: www.lordoftherings.net
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21. Junit Test Result
• The “==“ operator compares the reference of the variable.
• To fix it, override the Object.equals() method in Point
class.
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22. Override equals()
@Override
public boolean equals(Object obj){ //Parameter is of type Object
if(obj == null) return false;
if(obj == this) return true;
if(!(obj instanceof Point)) return false;
Point q = (Point) obj;
if(Math.abs(this.getX() - q.getX()) < 0.01 &&
Math.abs(this.getY() - q.getY()) < 0.01){
return true;
}
return false;
}
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23. Junit Test Result
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24. Part III : Writing a Test Suite
• In JUnit 3.8, you had to add a suite() method to
your classes to run all tests as a suite.
• With JUnit 4.0, you can use annotations instead.
• To run the PolygonImplTest, you write an empty
class with @RunWith and @Suite annotations.
• Very useful when you need to batch and run all the
test classes in one shot.
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25. Part III : All tests in one shot
package demo;
import org.junit.runner.RunWith;
import org.junit.runners.Suite;
@RunWith(Suite.class)
@Suite.SuiteClasses({PolygonImplTest.class})
public class PolygonImplTestSuite {
//Empty Class
}
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26. Part IV: Executing Tests
• Eclipse – Ctrl + F11 (run), F11 (debug)
• Command line
[ravikirn@xps demo]# javac -cp /usr/share/java/junit4.jar PolygonImpl.java Polygon.java
Point.java PolygonImplTest.java
[ravikirn@xps src]# java -cp /usr/share/java/junit4.jar:. org.junit.runner.JUnitCore
demo.PolygonImplTest
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27. Eclipse
• Auto resolve package dependency
– Ctrl + Shift + O
• Auto format code (helps when you paste
non-formatted code)
– Ctrl + Shift + F
• vim-like editing in Eclipse - vrapper
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28. vim / emacs
• Trust me, it‟s totally worth learning vim / emacs
• http://www.openvim.com/tutorial.html
• http://www.derekwyatt.org/vim/vim-tutorial-videos/
img source: http://www.thejach.com/view/2012/07/vims_learning_curve_is_wrong 28

29. Best Practices
• Test Everything that can possibly break.
• Test I/O, nulls and boundary conditions,
they are always the big culprits.
• Test Driven Development (TDD)
– TestCase  Code  Pass Test  Refactor
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30. Summary
• Testing • Self Study / Explore
– Unit Testing – How to test private and
– Integration Testing protected methods?
– System Testing
– How to test methods which
take input from console
• Junit (and | or) dump output to
– Initialize console ?
– Write Test Cases
– Batch Test Cases – How to test methods that
(TestSuite) don‟t return or print
– Execute Test Case anything to the console ?
– How to test exceptions ?
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32. Q&A
Many of the slides are attributed to Thomas Zimmermann
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