有效应用的设计模式与灵活的单元测试途径

发布: 2008-7-30 09:53 | 作者: 熊伟 | 来源: IBM | 查看: 53次 | 进入软件测试论坛讨论

Abstract Factory 是另一种被普遍运用的创建型模式，Abstract Factory 通过专门的 Factory Class 来封装对象创建的职责，并通过实现 Abstract Factory 来完成不同的创建逻辑。如果被测试单元所使用的外部对象是通过 Abstract Factory 创建的，则实现一个新的 Concrete Factory，并在此 Factory 中创建 Mock Objects 是一个比较好的解决办法。对于 Factory 本身，则可以在 setUp 测试的时候指定新的 Concrete Factory ；此外，借助依赖注入框架（如 Spring 的 BeanFactory），通过依赖注入的方式将 Factory 注入也是一种不错的解决方案。对于简单的依赖注入需求，可以考虑实现一个应用专有的依赖注入模块，或者实现一个简单的实现加载器，即根据配置文件载入相应的实现，从而无需修改应用代码，仅通过修改配置文件即可载入不同的实现，进而方便地修改程序的运行路径，执行单元测试。

下面的代码实现了一个简单的 InstanceFactory：

// refer to http://www.opensc-project.org/opensc-java/export/100/trunk/
// pkcs15/src/main/java/org/opensc/pkcs15/asn1/InstanceFactory.java
packagecom.instancefactory.demo;

importjava.lang.reflect.InvocationTargetException;
importjava.lang.reflect.Method;
importjava.lang.reflect.Modifier;

public class InstanceFactory {
    private final Method getInstanceMethod;
    
    public InstanceFactory(String type) { 
        Class clazz =null;
        try { 
            clazz = Class.forName(type);
            this.getInstanceMethod = clazz.getMethod("getInstance");
            if(!Modifier.isStatic(this.getInstanceMethod.getModifiers()) 
            || !Modifier.isPublic(this.getInstanceMethod.getModifiers()))
                throw new IllegalArgumentException(
                    "Method [" + clazz.getName() 
                    + ".getInstance(Object)] is not static public."); 
        } catch (NoSuchMethodException e) {
            throw new IllegalArgumentException(
                "Class [" + clazz.getName() 
                + "] has no static getInstance(Object) method.", e); 
        } catch (ClassNotFoundException e) {
            throw new IllegalArgumentException("Class [" + type + "] is not found"); 
        } 
    }

    public Object getInstance() {
        try{
            return this.getInstanceMethod.invoke(null); 
        } catch (InvocationTargetException e) {
            if( e.getCause() instanceof RuntimeException )
                throw (RuntimeException)e.getCause();
            throw new IllegalArgumentException(
                    "Method [" +this.getInstanceMethod 
                    + "] has thrown an checked exception.", e); 
        } catch( IllegalAccessException e) {
            throw new IllegalArgumentException(
                    "Illegal access to method [" 
                    +this.getInstanceMethod + "].", e); 
        } 
    }
    
    public Method getGetInstanceMethod() {
        return this.getInstanceMethod; 
    } 
}

以下代码演示了 InstanceFactory 的简单使用：

// BaseObjects.java
package com.instancefactory.demo;

public interface BaseObjects {
    voidfunc(); 
} 

 // OuterObjects.java

package com.instancefactory.demo;

public class OuterObjects implements BaseObjects {
    public static BaseObjects getInstance() {
        return new OuterObjects(); 
    }
    
    public void func() { 
        System.out.println("OuterObjects.func"); 
    } 
} 

// MockOuterObjects.java
package com.instancefactory.demo;
public class MockOuterObjects implements BaseObjects {
    public static BaseObjects getInstance() {
        return new MockOuterObjects(); 
    }
    
    public void func() { 
        System.out.println("MockOuterObjects.func"); 
    } 
 } 

// LogicToBeTested.java
packagecom.instancefactory.demo;
public class LogicToBeTested {
    public static final String PROPERTY_KEY= "BaseObjects";
    public void doSomething() { 
        // load configuration file and read the implementation class name of BaseObjects 
        // read it from properties to simplify the demo 
        // actually, the property file reader can be implemented by InstanceFactory 
        String impl = System.getProperty(PROPERTY_KEY); 
        InstanceFactory factory = new InstanceFactory(impl); 
        BaseObjects b = (BaseObjects)factory.getInstance(); 
        b.doSomething(); 
    } 
 } 

// LogicTest.java
packagecom.instancefactory.demo;
importjunit.framework.TestCase;
public class LogicTest extends TestCase { 
    LogicToBeTested c;
    protected void setUp() { 
        // set the property file of class map to a file for MockObjects, omitted 
        // use System.setProperty to simplify the demo 
        System.setProperty(LogicToBeTested.PROPERTY_KEY, 
                "com.instancefactory.demo.MockOuterObjects"); 
        c = new LogicToBeTested(); 
    }
    
    public void testDoSomething() { 
        c.doSomething(); 
    } 
 }