Java Mocking入门—使用Mockito

2014/03/10 | 分类：基础技术 | 0 条评论 | 标签：单元测试

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我们都会编写单元测试程序，但我们当前所面临的挑战是被测单元可能依赖于其他组件。而对于单元测试配置其他组件，绝对是过枉矫正。相反，我们可以使用Mocks框架代替其他组件，继续进行单元测试。

为了展现如何使用mock框架，我编写一个数据访问层(DAL)，该类对应用提供了一套API 接口来访问和修改数据库中的数据。之后在不需要连接数据库的情况下，对DAL类进行单元测试。数据库可以是本地数据库、远程数据库、文件系统或者任何可以储存和检索数据的地方。使用DAL类帮助我们将数据映射操作从应用代码中分离出来。

使用maven建立一个Java工程。

1	`mvn archetype:generate -DgroupId=info.sanaulla -DartifactId=MockitoDemo -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false`

以上操作建立了一个MockitoDemo文件夹，然后创建源文件和测试文件的整个目录结构。

考虑下面这个示例模型类：

package info.sanaulla.models;

import java.util.List;

/**

* Model class for the book details.

*/

public class Book {

private String isbn;

private String title;

private List<String> authors;

private String publication;

private Integer yearOfPublication;

private Integer numberOfPages;

private String image;

public Book(String isbn,

String title,

List<String> authors,

String publication,

Integer yearOfPublication,

Integer numberOfPages,

String image){

this.isbn = isbn;

this.title = title;

this.authors = authors;

this.publication = publication;

this.yearOfPublication = yearOfPublication;

this.numberOfPages = numberOfPages;

this.image = image;

}

public String getIsbn() {

return isbn;

}

public String getTitle() {

return title;

}

public List<String> getAuthors() {

return authors;

}

public String getPublication() {

return publication;

}

public Integer getYearOfPublication() {

return yearOfPublication;

}

public Integer getNumberOfPages() {

return numberOfPages;

}

public String getImage() {

return image;

}

操作Book模型类的DAL类：

package info.sanaulla.dal;

import info.sanaulla.models.Book;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.Collections;

import java.util.List;

/**

* API layer for persisting and retrieving the Book objects.

*/

public class BookDAL {

private static BookDAL bookDAL = new BookDAL();

public List<Book> getAllBooks(){

return Collections.EMPTY_LIST;

}

public Book getBook(String isbn){

return null;

}

public String addBook(Book book){

return book.getIsbn();

}

public String updateBook(Book book){

return book.getIsbn();

}

public static BookDAL getInstance(){

return bookDAL;

}

当前DAL层以上没有任何功能，我们将对这段代码TDD进行单元测试。DAL层可能与ORM映射API或者数据库API通讯，而我们不关心的这些API是如何设计的。

测试驱动DAL层

对单元测试和Java Mock有很多框架，对这个例子，我将选择JUnit做单元测试，Mockito作为Java mock。我们会在Maven的pom.xml文件中更新依赖属性。

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 <a href="http://maven.apache.org/maven-v4_0_0.xsd">http://maven.apache.org/maven-v4_0_0.xsd"</a>>

<modelVersion>4.0.0</modelVersion>

<groupId>info.sanaulla</groupId>

<artifactId>MockitoDemo</artifactId>

<packaging>jar</packaging>

<version>1.0-SNAPSHOT</version>

<name>MockitoDemo</name>

<url>http://maven.apache.org</url>

<dependencies>

<dependency>

<groupId>junit</groupId>

<artifactId>junit</artifactId>

<version>4.10</version>

<scope>test</scope>

</dependency>

<dependency>

<groupId>org.mockito</groupId>

<artifactId>mockito-all</artifactId>

<version>1.9.5</version>

<scope>test</scope>

</dependency>

</dependencies>

</project>

现在进行BookDAL类的单元测试。单元测试中，我们将注入mock数据到BookDAL类，因此我们可以不依赖数据源就可以完成API的测试。

最初我们有一个空的测试类:

public class BookDALTest {

public void setUp() throws Exception {

}

public void testGetAllBooks() throws Exception {

}

public void testGetBook() throws Exception {

}

public void testAddBook() throws Exception {

}

public void testUpdateBook() throws Exception {

}

我们将使用下面的setUp()函数把BookDAL类注入mock对象，并设置mock对象数据:

public class BookDALTest {

private static BookDAL mockedBookDAL;

private static Book book1;

private static Book book2;

@BeforeClass

public static void setUp(){

//Create mock object of BookDAL

mockedBookDAL = mock(BookDAL.class);

//Create few instances of Book class.

book1 = new Book("8131721019","Compilers Principles",

Arrays.asList("D. Jeffrey Ulman","Ravi Sethi", "Alfred V. Aho", "Monica S. Lam"),

"Pearson Education Singapore Pte Ltd", 2008,1009,"BOOK_IMAGE");

book2 = new Book("9788183331630","Let Us C 13th Edition",

Arrays.asList("Yashavant Kanetkar"),"BPB PUBLICATIONS", 2012,675,"BOOK_IMAGE");

//Stubbing the methods of mocked BookDAL with mocked data.

when(mockedBookDAL.getAllBooks()).thenReturn(Arrays.asList(book1, book2));

when(mockedBookDAL.getBook("8131721019")).thenReturn(book1);

when(mockedBookDAL.addBook(book1)).thenReturn(book1.getIsbn());

when(mockedBookDAL.updateBook(book1)).thenReturn(book1.getIsbn());

}

public void testGetAllBooks() throws Exception {}

public void testGetBook() throws Exception {}

public void testAddBook() throws Exception {}

public void testUpdateBook() throws Exception {}

}

在上面的setUp()方法中，我做了:

1. 创建一个BookDAL的mock对象

1	`BookDAL mockedBookDAL = mock(BookDAL.class);`

2. 存根带mock数据的BookDAL对象的API，这样无论何时调用API都可以返回mock数据。

//When getAllBooks() is invoked then return the given data and so on for the other methods.

when(mockedBookDAL.getAllBooks()).thenReturn(Arrays.asList(book1, book2));

when(mockedBookDAL.getBook("8131721019")).thenReturn(book1);

when(mockedBookDAL.addBook(book1)).thenReturn(book1.getIsbn());

when(mockedBookDAL.updateBook(book1)).thenReturn(book1.getIsbn());

填充剩余的测试方法:

package info.sanaulla.dal;

import info.sanaulla.models.Book;

import org.junit.BeforeClass;

import org.junit.Test;

import static org.junit.Assert.*;

import static org.mockito.Mockito.mock;

import static org.mockito.Mockito.when;