Advanced Unit Testing for Java By Denilson Nastacio Mastering Mock Objects

Your Host Denilson Nastacio 14 years in software development Quality Enthusiast Rational Unified Process practitioner RTP Scrolls ( http://rtpscrolls.blogspot.com ) SourcePatch ( http://sourcepatch.blogspot.com ) LinkedIn ( http://www.linkedin.com/in/nastacio )

Denilson Nastacio

14 years in software development

Quality Enthusiast

Rational Unified Process practitioner

RTP Scrolls ( http://rtpscrolls.blogspot.com )

SourcePatch ( http://sourcepatch.blogspot.com )

LinkedIn ( http://www.linkedin.com/in/nastacio )

Agenda Concepts Intercepting methods Declaring expectations Tools

Concepts

Intercepting methods

Declaring expectations

Tools

Different levels of abstraction Code logic Tests whether isolated methods respect their exposed contract Guarantees that there are no broken code paths No runtime dependencies: mock objects Integration test (by developer, not QA organization) Tests combination of classes and runtime environment Require runtime support Detect incompatibilities between components Residual code logic tests Function test (by developer, not QA organization) Real end-user scenarios Residual code logic and integration test. A C E D B A C E B A C E D B

Code logic

Tests whether isolated methods respect their exposed contract

Guarantees that there are no broken code paths

No runtime dependencies: mock objects

Integration test (by developer, not QA organization)

Tests combination of classes and runtime environment

Require runtime support

Detect incompatibilities between components

Residual code logic tests

Function test (by developer, not QA organization)

Real end-user scenarios

Residual code logic and integration test.

Ideal resource allocation Code logic Integration Function QA Function Test Development Dev QA System Test Runtime dependencies Cost per volume of code

The case against system dependencies on unit testing Complex Create user accounts, upgrade OS, install fixpacks, etc Slow Minutes to recycle servers between tests Unnecessary During development, you want to test the code, purge logic errors before starting test integration

Complex

Create user accounts, upgrade OS, install fixpacks, etc

Slow

Minutes to recycle servers between tests

Unnecessary

During development, you want to test the code, purge logic errors before starting test integration

Code logic test Classes tested in isolation Black box testing Based on declared interfaces, not actual implementation Guarantees that methods respect their declared interfaces Good to validate public APIs Bad for validating exceptions related to environment problems White box testing Based on implementation, usually due to incomplete specifications Typical of test written after the fact Concerned with exhaustive test of all lines in the actual source code Good to verify exception handling when combined with mock objects

Classes tested in isolation

Black box testing

Based on declared interfaces, not actual implementation

Guarantees that methods respect their declared interfaces

Good to validate public APIs

Bad for validating exceptions related to environment problems

White box testing

Based on implementation, usually due to incomplete specifications

Typical of test written after the fact

Concerned with exhaustive test of all lines in the actual source code

Good to verify exception handling when combined with mock objects

Mock environments for Java

Classes of mock environments Environment simulators Respond like the real environment Pros: Simulate complex behavior without environment dependencies Cons: Few simulators available, maintaining a simulator rivals the complexity of maintaining a real application Mock object frameworks Same interfaces as the real environment Developer must preset the mock objects with the expected responses Pros: Mock objects can be generated quickly for any environment Cons: Presetting mock objects for unit tests may require lots of code

Environment simulators

Respond like the real environment

Pros: Simulate complex behavior without environment dependencies

Cons: Few simulators available, maintaining a simulator rivals the complexity of maintaining a real application

Mock object frameworks

Same interfaces as the real environment

Developer must preset the mock objects with the expected responses

Pros: Mock objects can be generated quickly for any environment

Cons: Presetting mock objects for unit tests may require lots of code

Mock libraries JMockit Instructs the JVM to replace calls to any method with code under your control One-two punch with JMock against bunkered initialization within the production code, such as calls to constructors or static methods Use JMockit to intercept calls to static methods deep into the production code and return JMock pre-programmed objects. http://jmockit.dev.java.net JMock Pre-program objects to expect calls and return values of your choice Instruct the production code to “talk to” mocked object instead of actual system dependency Mocks interfaces and classes. http://www.jmock.org

JMockit

Instructs the JVM to replace calls to any method with code under your control

One-two punch with JMock against bunkered initialization within the production code, such as calls to constructors or static methods

Use JMockit to intercept calls to static methods deep into the production code and return JMock pre-programmed objects.

http://jmockit.dev.java.net

JMock

Pre-program objects to expect calls and return values of your choice

Instruct the production code to “talk to” mocked object instead of actual system dependency

Mocks interfaces and classes.

http://www.jmock.org

Anatomy of JMock in a test fixture @Test public void testTransferFunds() throws Exception { org.jmock.Mockery context = new Mockery(); context.setImposteriser(ClassImposteriser. INSTANCE ); final float testAmount = 300; final BankAccount sourceAccount = context.mock(BankAccount. class , "source" ); final BankAccount targetAccount = context.mock(BankAccount. class , "target" ); org.jmock.Expectations expect = new Expectations() { { one(sourceAccount).withdraw(testAmount); one(targetAccount).deposit(testAmount); } }; context.checking(expect); Transaction tx = new Transaction(); tx.transferFunds(testAmount, sourceAccount, targetAccount); context.assertIsSatisfied(); } Create mock Context Create mock instances Programs mock instances Adds expectation to mock context. Asks context whether all expectations were met.

@Test

public void testTransferFunds() throws Exception {

org.jmock.Mockery context = new Mockery();

context.setImposteriser(ClassImposteriser. INSTANCE );

final float testAmount = 300;

final BankAccount sourceAccount = context.mock(BankAccount. class , "source" );

final BankAccount targetAccount = context.mock(BankAccount. class , "target" );

org.jmock.Expectations expect = new Expectations() {

{

one(sourceAccount).withdraw(testAmount);

one(targetAccount).deposit(testAmount);

}

};

context.checking(expect);

Transaction tx = new Transaction();

tx.transferFunds(testAmount, sourceAccount, targetAccount);

context.assertIsSatisfied();

}

Anatomy of JMockit in a test fixture – Inlined mock @Mocked private final BankSOAUtil unused = null ; @Test public void testBankAccountSOA() throws Exception { String inputDir = "abc" ; final String inputFile = "AndrewBankAccountData.xml" ; new mockit.Expectations() { { BankSOAUtil. getInputStream ((URL)withNotNull()); returns( new FileInputStream(inputFile)); } }; // Bank account constructor reads its configuration using // BankSOAUtil.getInputStream BankAccount bc = new BankAccount( "userid" , "password" ); Assert. assertEquals ( "Andrew" , bc.getCustomerName()); } Inlined mocked expectation Programming the expectation Marking class to be mocked

@Mocked private final BankSOAUtil unused = null ;

@Test

public void testBankAccountSOA() throws Exception {

String inputDir = "abc" ;

final String inputFile = "AndrewBankAccountData.xml" ;

new mockit.Expectations() {

{

BankSOAUtil. getInputStream ((URL)withNotNull());

returns( new FileInputStream(inputFile));

}

};

// Bank account constructor reads its configuration using

// BankSOAUtil.getInputStream

BankAccount bc = new BankAccount( "userid" , "password" );

Assert. assertEquals ( "Andrew" , bc.getCustomerName());

}

Anatomy of JMockit in a test fixture – Using a mock class public void testBankAccountSOA() throws Exception {s Mockit.setUpMocks(MockBankSOAUtil.class); String inputFile = "AndrewBankAccountData.xml"; // Bank account constructor reads its configuration using // BankSOAUtil. getInputStream BankAccount bc = new BankAccount(...); Assert.assertEquals("Andrew", bc.getCustomerName()); Mockit.tearDownMocks(); } @MockClass(realClass = BankSOAUtil.class) public static class MockBankSOAUtil { private static String inputFile = null; @Mock(invocations = 1) public static InputStream getInputStream (URL inputUrl) throws IOException { return new FileInputStream(inputFile) ; } public static void setInputFile(String inputFile) { MockDogearUtil.inputFile = inputFile ; } } Instructs the JVM about the mock classes to be used Instructs the JVM to stop using JMockit mocks. Declares the production class to be mocked Indicates which methods of the production class should be mocked

public void testBankAccountSOA() throws Exception {s

Mockit.setUpMocks(MockBankSOAUtil.class);

String inputFile = "AndrewBankAccountData.xml";

// Bank account constructor reads its configuration using

// BankSOAUtil. getInputStream

BankAccount bc = new BankAccount(...);

Assert.assertEquals("Andrew", bc.getCustomerName());

Mockit.tearDownMocks();

}

@MockClass(realClass = BankSOAUtil.class)

public static class MockBankSOAUtil {

private static String inputFile = null;

@Mock(invocations = 1)

public static InputStream getInputStream (URL inputUrl)

throws IOException {

return new FileInputStream(inputFile) ;

}

public static void setInputFile(String inputFile) {

MockDogearUtil.inputFile = inputFile ;

}

}

Which one should I use? JMockit Can intercept any call to the JVM Added many improvements to expectation support during 2009 Supports bytecode level coverage metrics My new favorite JMock Used to have better control over behavior of mocked object My former favorite Needs production code to provide “entry points” to receive the mocked objects

JMockit

Can intercept any call to the JVM

Added many improvements to expectation support during 2009

Supports bytecode level coverage metrics

My new favorite

JMock

Used to have better control over behavior of mocked object

My former favorite

Needs production code to provide “entry points” to receive the mocked objects

Building mock expectations Required versus allowed Is it important that the mocked method be actually called? JMock: allowing/ignored/one JMockit: Expectations, Verifications, and sub-classes Specific versus loose Is it important that the mocked method be actually called with a specific parameter? Both JMock and JMockit offer out-of-the-box matchers for concepts like 'same value', 'same class', 'inherited from a class', 'null', 'not null', and others

Required versus allowed

Is it important that the mocked method be actually called?

JMock: allowing/ignored/one

JMockit: Expectations, Verifications, and sub-classes

Specific versus loose

Is it important that the mocked method be actually called with a specific parameter?

Both JMock and JMockit offer out-of-the-box matchers for concepts like 'same value', 'same class', 'inherited from a class', 'null', 'not null', and others

When results matter – 1 of 3 What if results from a dependency matter? public class ExternalClass { public String somethingWithAReturnValue(String input) { return "DEF" ; }

What if results from a dependency matter?

public class ExternalClass {

public String somethingWithAReturnValue(String input) {

return "DEF" ;

}

When results matter – JMock 2 of 3 final ExternalClass ecMock = context.mock(ExternalClass. class ); org.jmock.Expectations expect = new org.jmock.Expectations() { { one(ecMock).somethingWithAReturnValue( &quot;specific value&quot; ); will( returnValue ( &quot;someReturnValue&quot; )); } }; final ExternalClass ecMock = context.mock(ExternalClass. class ); org.jmock.Expectations expect = new org.jmock.Expectations() { { one(ecMock).somethingWithAReturnValue(with( any (String. class ))); will( returnValue ( &quot;someReturnValue&quot; )); } }; Use with(any(Class <T> type)) to instruct the JMock mock to ignore input parameters

final ExternalClass ecMock = context.mock(ExternalClass. class );

org.jmock.Expectations expect = new org.jmock.Expectations() {

{

one(ecMock).somethingWithAReturnValue( &quot;specific value&quot; );

will( returnValue ( &quot;someReturnValue&quot; ));

}

};

final ExternalClass ecMock = context.mock(ExternalClass. class );

org.jmock.Expectations expect = new org.jmock.Expectations() {

{

one(ecMock).somethingWithAReturnValue(with( any (String. class )));

will( returnValue ( &quot;someReturnValue&quot; ));

}

};

When results matter – Jmockit - 3 of 3 new mockit.Expectations () { ExternalClass EcMock; { ecMock.somethingWithAReturnValue( &quot;specific value&quot; ); returns( &quot;someReturnValue&quot; )); } }; new mockit.Expectations () { ExternalClass EcMock; { ecMock.somethingWithAReturnValue(withAny( &quot;&quot; ); returns( &quot;someReturnValue&quot; )); } }; Use withAny(Class <T> type)) to instruct the JMockit mock to ignore input parameters

new mockit.Expectations () {

ExternalClass EcMock;

{

ecMock.somethingWithAReturnValue( &quot;specific value&quot; );

returns( &quot;someReturnValue&quot; ));

}

};

new mockit.Expectations () {

ExternalClass EcMock;

{

ecMock.somethingWithAReturnValue(withAny( &quot;&quot; );

returns( &quot;someReturnValue&quot; ));

}

};

Great companion tools DDTUnit http://ddtunit.sourceforge.net/ Cobertura http://cobertura.sourceforge.net/ Note: JMockit has its own code coverage support

DDTUnit

http://ddtunit.sourceforge.net/

Cobertura

http://cobertura.sourceforge.net/

Note: JMockit has its own code coverage support