java - 如何使用 when()... 解决此 Mockito MissingMethodInitationException？

Question

在 Eclipse 中，使用 junit 和 Mockito。我试图测试一个方法是否返回特定大小的列表，但出现以下错误:

org.mockito.exceptions.misusing.MissingMethodInvocationException: when() requires an argument which has to be 'a method call on a mock'. For example: when(mock.getArticles()).thenReturn(articles);

Also, this error might show up because: 1. you stub either of: final/private/equals()/hashCode() methods. Those methods cannot be stubbed/verified. 2. inside when() you don't call method on mock but on some other object.

我的测试:

class ValidateBookResultsTests {

public static ArrayList<Book> searchResults = new ArrayList<Book>();
public static List<Book> topFive;
public static ArrayList<String> authors = new ArrayList<String>();

public static Book book1;
public static Book book2;
public static Book book3;
public static Book book4;
public static Book book5;
public static Book book6;

@BeforeEach
public void setUp() {
    book1 = new Book("title1", authors, "publisher1");
    book2 = new Book("title2", authors, "publisher2");
    book3 = new Book("title3", authors, "publisher3");
    book4 = new Book("title4", authors, "publisher4");
    book5 = new Book("title5", authors, "publisher5");
    book6 = new Book("title6", authors, "publisher6");

    searchResults.add(book1);
    searchResults.add(book2);
    searchResults.add(book3);
    searchResults.add(book4);
    searchResults.add(book5);
    searchResults.add(book6);
}

@Test
public void returnFiveBooksFromSearchResults() {
    authors.add("John Doe");
    authors.add("Bill Gates");

    BookSearch mockBookSearch = Mockito.mock(BookSearch.class);
    Mockito.when(mockBookSearch.returnFiveBooks(searchResults)).thenReturn(topFive);

    System.out.println("return books: " + mockBookSearch.returnFiveBooks(searchResults));
    System.out.println("top: "+ topFive);

    assertEquals(topFive.size(), 5);
 }
}

我的相关代码:

public static List<Book> returnFiveBooks(ArrayList<Book> searchResults) {
  Collections.shuffle(searchResults);
  topFive = searchResults.subList(0, 5);

  printFiveResults();

  return topFive; }

我读过其他解决方案，说要创建一个模拟类/对象，我相信我已经完成了“BookSearch mockBookSearch = Mockito.mock(BookSearch.class);”

我错过了什么？

Answer 1

错误消息告诉您，您的方法调用不是模拟上的方法调用。

org.mockito.exceptions.misusing.MissingMethodInvocationException: 
when() requires an argument which has to be 'a method call on a mock'.
For example:
    when(mock.getArticles()).thenReturn(articles);

为什么？因为您正在尝试模拟 静态方法。

Mockito.when(mockBookSearch.returnFiveBooks(searchResults)).thenReturn(topFive);

这相当于:

Mockito.when(BookSearch.returnFiveBooks(searchResults)).thenReturn(topFive);

Mockito 不能用于模拟静态方法。

这解释了您收到的错误。但您的代码更根本的问题是您有一个正在测试的方法，并在测试中模拟它。这毫无意义。您应该模拟您的方法使用的协作者(您的代码中没有)。要测试 returnFiveBooks 你根本不需要模拟:

@Test
public void returnFiveBooksFromSearchResults() {
    var topFive = BookSearch.returnFiveBooks(searchResults);
    assertEquals(topFive.size(), 5);
}

编辑:从 Mockito 3.4.0 开始支持模拟静态方法