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Unit TestingObject-Oriented

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Unit Testing Object-Oriented SoftwareWith JUnit, JMock, and the Java Reflection API

CSCE361: Software Engineering

University of NebraskaLincoln

September 15, 2010

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From Last Week

Verification techniques can be static, dynamic, or mixed.

Testing, an example of dynamic verification, exercisessystem behaviors and evaluates the results.

Among the various types of testing, unit testing usuallycomes first in the software life cycle.

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Unit Testing

Unit testing focuses on small pieces of code in isolation,usually individual classes.

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Properties of the Ideal Test Suite

SoundnessWe claim that the system is buggy only

when it really is.CompletenessWe claim that the system is correctonly when it really is.

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Advantages of Unit Testing

Soundness: Its easier to determine the oracle for a

smaller piece of code.Completeness: We can easily test methods that aredifficult to reach in the system context.

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Disadvantages of Unit Testing

Soundness: We may uncover faults that can never be

exposed at the system level.Completeness: We will miss bugs in the way units arecombined.

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Properties of the Ideal Test Suite (cont.)

TraceabilityGiven a failure, it takes little effort to findthe underlying fault.

FeasibilityThe cost to implement and use the testsuite is minimal.

MaintainabilityWhen the system changes, test suiteupdates arent overly costly.

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Advantages of Unit Testing (cont.)

Traceability: If we find a failure, we know that the faultis within the unit.

Feasibility: We can run the tests early, before the entiresystem is assembled.

Maintainability: If a unit is unchanged, its tests survive.

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Disadvantages of Unit Testing (cont.)

Feasibility: Each test only exercises a few behaviors, sowe must write many.

Maintainability: The test cases must change wheneverthe implementation changes, even if the systembehavior is unaffected.

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Outline

1 Motivation

2 Design

3 Implementation

4 Demo

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Overview of Unit Testing

1 Isolate the unit

2 Setup the inputs

3 Execute the unit

4 Verify the outputs

5 Tear-down

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Isolation

Problem: Units might depend on others.

Solution: Usually, we mock-up the other units: wereplace the real objects with fake ones and script theirbehavior.

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I l


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Isolation

Problem: Units might depend on others.

Solution: Usually, we mock-up the other units: wereplace the real objects with fake ones and script theirbehavior.

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I S d T d


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Input Setup and Tear-down

Problem: Test cases often share setup and tear-down

procedures.Solution: We group common code into fixtures.

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U i T iI S d T d


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Input Setup and Tear-down

Problem: Test cases often share setup and tear-down

procedures.Solution: We group common setup and tear-down codeinto fixtures.

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U it T tiE ti d V ifi ti


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Execution and Verification

Problem: The test case cannot call methods withaccess restrictions (private, protected, etc.). Likewise,

the results of a test might include nonpublic fields.

Solution: We change the method and field visibility fortesting only.

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Unit TestingE ti d V ifi ti


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Execution and Verification

Problem: The test case cannot call methods withaccess restrictions (private, protected, etc.). Likewise,

the results of a test might include nonpublic fields.

Solution: We change the method and field visibility fortesting only.

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Unit TestingOutline


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Outline

1 Motivation

2 Design

3 Implementation

4 Demo

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Unit TestingOverview of Unit Testing


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Overview of Unit Testing

1 Isolate the unit

2 Setup the inputs

3 Execute the unit

4 Verify the outputs

5 Tear-down

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Unit TestingPreliminaries


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Preliminaries

1 import java.lang.reflect.*;2 import org.junit.*;

3 import org.junit.runner.*;

4 import org.jmock.*;

5 import org.jmock.integration.junit4.*;

7 import static org.junit.Assert.*;

9 @RunWith(JMock.class)

10 public class ExampleTester{

11 //The unit under test

12 protected ExampleUnit exampleUnit;13 //...

14 }

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Unit TestingIsolation


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U gObject-Oriented

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Isolation

1 Mockery mockery=new JUnit4Mockery();

2 OtherUnit otherUnit=mockery.mock(OtherUnit.class);

3 mockery.checking(new Expectations(){{

4 //first, expect one invocation of foo()

5

oneOf(otherUnit).foo();6 //have it return 1123

7 will(returnValue(1123));

8 //then, expect one invocation of bar(9)

9 oneOf(otherUnit).bar(9);

10 //...

11 }});

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Unit TestingInput Setup


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gObject-Oriented

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Input Setup

1 protected Input input;

3 @Before

4 public void setup(){

5 //(mockery code goes here...)

6 //create the unit under test7 exampleUnit=new ExampleUnit(otherUnit);

8 //create input values

9 input=new Input();

10 input.setBaz(-106);

11 input.setQuux(83);12 }

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Unit TestingExecution


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Execution

1 @Test

2 public void testXyzzy(){

3 Output result=exampleUnit.xyzzy(input);4 //...

5 }

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Unit TestingExecution (alternative)


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Execution (alternative)

1 @Test

2 public void testXyzzy() throws Exception{

3 Method xyzzy=exampleUnit.getClass().

getDeclaredMethod("xyzzy",Input.class);4 xyzzy.setAccessible(true);

5 Output result=xyzzy.invoke(exampleUnit,input);

6 //...

7 }

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Unit TestingObj O i dVerification


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Verification

1 @Test

2 public void testXyzzy(){

3 //...

4 assertEquals("Xyzzy should always return anOutput of length 2",2,result.getSize());

5 assertNotNull("The plugh field of xyzzys result

should never be null",result.getPlugh());

6 }

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Unit TestingObj t O i t dTear-down


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Tear down

1 @After

2 public void teardown() throws IOException{

3 //free outstanding resources4 input.close();

5 }

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Unit TestingObject OrientedOutline


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Unit TestingObject OrientedFor Next Time


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Motivation

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DemoWhich units should we test?

What test cases should we use?When are we done testing?

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Unit TestingObject-OrientedJump to Slide (130)


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