Java Mocking入门—使用Mockito

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。

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 for JUnit -->
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.10</version>
      <scope>test</scope>
    </dependency>
    <!-- Dependency for Mockito -->
    <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

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;

import java.util.Arrays;
import java.util.List;

public class BookDALTest {

  private static BookDAL mockedBookDAL;
  private static Book book1;
  private static Book book2;

  @BeforeClass
  public static void setUp(){
    mockedBookDAL = mock(BookDAL.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");

    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());

  }

  @Test
  public void testGetAllBooks() throws Exception {

    List<Book> allBooks = mockedBookDAL.getAllBooks();
    assertEquals(2, allBooks.size());
    Book myBook = allBooks.get(0);
    assertEquals("8131721019", myBook.getIsbn());
    assertEquals("Compilers Principles", myBook.getTitle());
    assertEquals(4, myBook.getAuthors().size());
    assertEquals((Integer)2008, myBook.getYearOfPublication());
    assertEquals((Integer) 1009, myBook.getNumberOfPages());
    assertEquals("Pearson Education Singapore Pte Ltd", myBook.getPublication());
    assertEquals("BOOK_IMAGE", myBook.getImage());
  }

  @Test
  public void testGetBook(){

    String isbn = "8131721019";

    Book myBook = mockedBookDAL.getBook(isbn);

    assertNotNull(myBook);
    assertEquals(isbn, myBook.getIsbn());
    assertEquals("Compilers Principles", myBook.getTitle());
    assertEquals(4, myBook.getAuthors().size());
    assertEquals("Pearson Education Singapore Pte Ltd", myBook.getPublication());
    assertEquals((Integer)2008, myBook.getYearOfPublication());
    assertEquals((Integer)1009, myBook.getNumberOfPages());

  }

  @Test
  public void testAddBook(){
    String isbn = mockedBookDAL.addBook(book1);
    assertNotNull(isbn);
    assertEquals(book1.getIsbn(), isbn);
  }

  @Test
  public void testUpdateBook(){

    String isbn = mockedBookDAL.updateBook(book1);
    assertNotNull(isbn);
    assertEquals(book1.getIsbn(), isbn);
  }
}

使用maven命令: mvn test进行测试。输出如下:

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running info.sanaulla.AppTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.029 sec
Running info.sanaulla.dal.BookDALTest
Tests run: 4, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.209 sec

Results :

Tests run: 5, Failures: 0, Errors: 0, Skipped: 0

至此,通过使用mock框架,在不用实际配置数据源的情况下,就可以测试DAL类。

原文链接: dzone 翻译: ImportNew.com - liken
译文链接: http://www.importnew.com/10083.html
[ 转载请保留原文出处、译者和译文链接。]

关于作者: liken

(新浪微博:@lihenair

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