Test Units Containing Static Dependencies · Static Dependencies 2010-09-04 Wednesday, September 8, 2010. William Rowden Co-founded Agile Software company (Gray Hill Solutions, Inc.)

Test Units Containing Static Dependencies

2010-09-04

Wednesday, September 8, 2010

William Rowden

Co-founded Agile Software company (Gray Hill Solutions, Inc.) in 2001


SolutionsIQWednesday, September 8, 2010

SolutionsIQAgile Software Development

Agile Training

Agile Consulting

• Agile Coaching

• Agile Team Services

• Agile Enterprise Rollouts


Hobbies

Love to travel

Hablo español(I speak Spanish,我会说西班牙语)

我会说一点儿普通话


HistoryBASIC, QBasic, Visual Basic, VBA, Visual Basic.NET, VBScript

Pascal

S+, R

FORTRAN

make, bash


LanguagesC++, C# 3.5 (with XAML)

Python

Perl (with HTML)

SQL

Java


AgendaWednesday, September 8, 2010

ProblemWednesday, September 8, 2010

ProblemTest a system containing a

hidden dependency on a static method call


Code Sample

package com.solutionsiq.wrowden;

public class SystemUnderTest { public ReturnValue methodWithDependecies() { ReturnValue returnValue = Library.staticMethod(); returnValue.doSomething(); return returnValue; }}

Library.staticMethod()


Problem


import static org.junit.Assert.assertEquals;import org.junit.Test;

public class WhenSystemUnderTestHasStaticDependencies {

@Test public void shouldBreakDependency() { final ReturnValue testValue = new ReturnValue(); final SystemUnderTest systemUnderTest = new SystemUnderTest(); assertEquals ("Method gets value from environment.", testValue, systemUnderTest.methodWithDependencies()); }}


Problem一个问题...


Hidden Dependencies

Internally created objects

Static methods of other classes

Extension methods

Singletons

Static methods of other classes


Hidden Dependencies - Potential Problems

early infrastructure choice

set up time

tight coupling

slow tests


SolutionsWednesday, September 8, 2010

Design SolutionsWednesday, September 8, 2010

Extract & OverrideWednesday, September 8, 2010

Working Effectively with Legacy

Code


EclipseRefactor


Extract & Override Call


public class SystemUnderTest { public ReturnValue methodWithDependencies() { final ReturnValue returnValue = extractedStaticMethod(); returnValue.doSomething(); return returnValue; } protected ReturnValue extractedStaticMethod() { return Library.staticMethod(); }}


Eclipse SourceWednesday, September 8, 2010

Extract & Override Callpackage com.solutionsiq.wrowden;

import static org.junit.Assert.assertEquals;import org.junit.Test;

public class WhenSystemUnderTestHasStaticDependencies {

@Test public void shouldBreakDependency() { final ReturnValue testValue = new ReturnValue(); final SystemUnderTest systemUnderTest = new SystemUnderTest() {

@Override protected ReturnValue extractedStaticMethod() { return testValue; } }; final ReturnValue actualValue = systemUnderTest.methodWithDependencies(); assertEquals("Method gets value from environment.", testValue, actualValue); }}


Result 结果


Extract & Override CallAdvantages:

+ clear

+ fast

+ wide application

Disadvantages:

- hidden bugs

- indirection performance

- multiple methods

- production code policy

好处坏处


VerificationState:

ReturnValue

Behavior:

Library.staticMethod


Mock ObjectWednesday, September 8, 2010

ChihuahuaIn Mexico I discussed how to turn a class into an object.


Design Patterns:

Elements of Reusable Object-

Oriented Software


Interface

“Program to an interface, not an implementation.”

--Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides; Design Patterns: Elements of Reusable Object-Oriented Software


Adapter Pattern

“Clients call operations on an Adapter instance. In turn, the adapter calls Adaptee operations that carry out the request.”


The Art of Unit Testing


Mock Library


Interface


public interface AdaptableLibrary {

ReturnValue staticMethod();

}


EasyMock

import static org.easymock.EasyMock.createMock;import static org.easymock.EasyMock.expect;import static org.easymock.EasyMock.replay;import static org.easymock.EasyMock.verify;


Test-Driven Development

Fix failing test by calling mock Library

Real system calls Library adapter


Dependency Injection


public class SystemUnderTest { public ReturnValue methodWithDependencies(AdaptableLibrary library) { final ReturnValue returnValue = library.staticMethod(); returnValue.doSomething(); return returnValue; }}


Adapter Pattern


public class LibraryAdapter implements AdaptableLibrary {

@Override public ReturnValue staticMethod() { return Library.staticMethod(); }}


Result 结果


MockingAdvantages:

+ easy

+ readable

Disadvantages:

- less readable setup

- could require many mocks

- changed static method

好处坏处


Test SolutionsWednesday, September 8, 2010

西安钟楼In China I discussed test

strategies.


Test Techniques

if (testableCode = goodCode) {

// try dependency injection

// try mocking

}

testableCode = goodCode


Test Techniques

if (goodCode != testableCode) {

// try class loader

// try Aspect-Oriented Programming

}

goodCode = testableCode!


Class LoaderWednesday, September 8, 2010


import static org.junit.Assert.assertEquals;

@RunWith(PowerMockRunner.class)@PrepareForTest(Library.class)public class WhenSystemUnderTestHasStaticDependencies {

@Test public void shouldBreakDependency() { final ReturnValue testValue = new ReturnValue(); final SystemUnderTest systemUnderTest = new SystemUnderTest(); PowerMock.mockStatic(Library.class); EasyMock.expect(Library.staticMethod()).andReturn(testValue); PowerMock.replay(Library.class); assertEquals("Method gets value from environment.", testValue, systemUnderTest.methodWithDependencies()); PowerMock.verify(Library.class); }}

PowerMock


Result 结果


Class LoadersAdvantages:

+ removes external dependency

+ tests code using a third-party API

Disadvantages:

- doesn’t improve code design

- inhibits useful feedback

好处坏处


Aspect-Oriented Programming


Deciding WhichAre there bad smells in the code?

Can you improve the design of the existing code?

How many hidden dependencies are there?

Is performance a problem?

Is the call too simple to break? Or would overriding hide bugs?


Questions?


Documents

Test Units Containing Static Dependencies · Static Dependencies 2010-09-04 Wednesday, September 8, 2010. William Rowden Co-founded Agile Software company (Gray Hill Solutions, Inc.)