我們都編寫了單元測試，但是有時我們面臨的挑戰是被測單元可能依賴于其他組件。 并且配置其他組件進行單元測試絕對是一個過大的選擇。 相反，我們可以使用Mocks代替其他組件，并繼續進行單元測試。

為了說明如何使用模擬，我有一個數據訪問層（DAL），基本上是一個類，為應用程序提供API，以供應用程序訪問和修改數據存儲庫中的數據。 然后，我對DAL進行單元測試，而實際上無需連接到數據存儲庫。 數據存儲庫可以是本地數據庫或遠程數據庫，也可以是文件系統，也可以是我們可以存儲和檢索數據的任何位置。 DAL類的使用有助于我們將數據映射器與應用程序代碼分開。

讓我們使用maven創建一個Java項目。

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

上面創建了一個文件夾MockitoDemo，然后為源文件和測試文件創建了整個目錄結構。

考慮此示例的以下模型類：

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;} }

用于對Book模型類進行操作的DAL類為：

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;} }

上面的DAL層目前沒有功能，我們將對該單元代碼（ TDD ）進行單元測試。 DAL層可能與我們在設計API時不關心的ORM映射器或數據庫API通信。

測試DAL層

Java中有許多用于單元測試和模擬的框架，但是在這個示例中，我將選擇JUnit用于單元測試，選擇Mockito用于模擬 。 我們將不得不更新Maven的pom.xml中的依賴項

<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 http://maven.apache.org/maven-v4_0_0.xsd"><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>

現在讓單元測試BookDAL 。 在單元測試期間，我們會將模擬數據注入BookDAL中，以便我們無需依賴數據源即可完成API的測試。

最初，我們將有一個空的測試類：

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 {} }

我們將把模擬的BookDAL和模擬的數據注入到setUp() ，如下所示：

public class BookDALTest {private static BookDAL mockedBookDAL;private static Book book1;private static Book book2;@BeforeClasspublic static void setUp(){//Create mock object of BookDALmockedBookDAL = 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，我有：

創建了BookDAL的模擬對象 BookDAL mockedBookDAL = mock(BookDAL.class);

在BookDAL的API中添加模擬數據，以便在調用API時返回模擬數據。 //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());

填充其余的測試，我們得到：

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;@BeforeClasspublic 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());}@Testpublic 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());}@Testpublic 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());}@Testpublic void testAddBook(){String isbn = mockedBookDAL.addBook(book1);assertNotNull(isbn);assertEquals(book1.getIsbn(), isbn);}@Testpublic void testUpdateBook(){String isbn = mockedBookDAL.updateBook(book1);assertNotNull(isbn);assertEquals(book1.getIsbn(), isbn);} }

可以使用maven命令運行測試： mvn test 。 輸出為：

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

因此，我們已經能夠測試DAL類，而無需使用模擬實際配置數據源。

參考：來自Experiences Unlimited博客的JCG合作伙伴 Mohamed Sanaulla的Mockito 使用Java進行Mocking入門 。

翻譯自: https://www.javacodegeeks.com/2014/02/getting-started-with-mocking-in-java-using-mockito.html

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