测试静态方法，该方法需要模拟成员方法并使用PowerMockito抑制单例构造函数

Question

我想测试一个静态方法（例如HobbyUtil.java:shareReadContext(int lineNumber)），该方法将要求Singleton类（例如Shelf.java）获取对象（例如Book）以进一步获取值（例如上下文）返回的对象。

但是，在模拟案例执行期间，该Singleton类（即Shelf.java）的ctor将触发链中的其他几个Singleton类（例如LibraryA.java）；并且其中之一会触发java.lang.ExceptionInInitializerError。

我认为嘲笑/监视那些不相关的Singleton类超出了Mock Test的精神，因为它们与我的测试范围无关。

因此，我决定取消此Singleton类（即Shelf.java）的私有ctor，只让该类中的getter方法（即getBook()）返回具有我喜欢的行为的模拟对象，该对象将与我的行为完全匹配测试用例。

我遇到的问题是，我通过以下链接成功抑制了[[Shelf.java的ctor：suppress a singleton constructor in java with powermock

但是我无法弄清楚让此getter方法返回我想要的东西（即返回一个模拟对象）的方法。

我正在使用的

PowerMockito，hamcrest和JUnit的版本在此处列出以供参考：

<dependency><groupId>org.powermock</groupId><artifactId>powermock-module-junit4</artifactId><version>1.7.0</version><scope>test</scope></dependency>  
<dependency><groupId>org.powermock</groupId><artifactId>powermock-api-mockit02</artifactId><version>1.7.0</version><scope>test</scope></dependency>
<dependency><groupId>org.hamcrest</groupId><artifactId>hamcrest-all</artifactId><version>1.3</version><scope>test</scope></dependency>
<dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version><scope>test</scope></dependency>

[我还用下面的示例类复制了案例，以显示遇到的问题（HobbyUtilTest.java是我的测试案例的类：]
假设应用程序中有5个Java类：
public interface Book {
    public String getContext(int lineNumber);
}

public class Shelf {

    private static final Shelf shelf = new Shelf();
    private String BOOK_NAME = "HarryPotter";
    private Book book = null;

    private Shelf() {
        book = LibraryA.getInstance().getBook(BOOK_NAME);
        // many relatively complicated logics are here in actual class ... 
        // I want to suppress this ctor 
    }

    public static Shelf getInstance() {
        return shelf;
    }

    public Book getBook() {
        return book;  // I want to return my mocked object while calling this method in test case
    }

}

public class HobbyUtil {

    public static String shareReadContext(int lineNumber){
        String context = "";
        Book book = Shelf.getInstance().getBook();

        for (int i = 0 ; i < lineNumber; i++) {
            context += book.getContext(i);
        }
        return context;
    }

    private HobbyUtil() {}
}

public class LibraryA {
    private static final LibraryA library = new LibraryA();
    private Book book;

    private LibraryA() {
        throw new java.lang.ExceptionInInitializerError();
    }

    public static LibraryA getInstance() {
        return library;
    }

    public Book getBook(String bookName) {
        return book;
    }
}

public class BookImpl implements Book{

    private String bookName = null;

    BookImpl(String bookName){
        this.bookName = bookName;
    }

    @Override
    public String getContext(int lineNumber) {
        return lineNumber + ": Context";
    }
}

并且我会用shareReadContext(int lineNumber)测试HobbyUtil.java中的静态方法HobbyUtilTest.java
import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.mockito.ArgumentMatchers.anyInt;
import static org.powermock.api.mockito.PowerMockito.when;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

@RunWith(PowerMockRunner.class)
@PrepareForTest(value = { Shelf.class })
public class HobbyUtilTest {

    @Test
    public void testShareReadContext() throws Exception {

        Book mockBook = PowerMockito.mock(Book.class);
        when(mockBook.getContext(anyInt())).thenReturn("context for test");

        PowerMockito.suppress(PowerMockito.constructor(Shelf.class));
        //PowerMockito.spy(Shelf.class);
        //when(Shelf.getInstance().getBook()).thenReturn(mockBook); // does not work
        //PowerMockito.doReturn(mockBook).when(Shelf.getInstance().getBook()); // does not work
        //PowerMockito.when(Shelf.class, "getBook").thenReturn(mockBook); // does not work
        //TODO any approach for it?

        String context = HobbyUtil.shareReadContext(1);
        assertThat(context, is("context for test"));
    }
}

[任何人都可以帮助建议我如何让Book book = Shelf.getInstance().getBook();中的HobbyUtil.java行返回我的模拟对象（即mockBook）？

Answer 1

假设您的Shelf类位于程序包test中，这应该有效：