使用 PowerMockito 模拟装饰的流

Question

所以我有一个类，它在构造函数中获取一个输出流，并在方法中从中创建PrintWriter。问题是我如何让这个 PrintWriter 来验证它？

Example public Class(OutputStream output) {}
public void foo() {
  PrintWriter writer = new PrintWriter(output);
}

我尝试做的是：

PrintWriter writer = PowerMockito.mock(PrintWriter.class)
PowerMockito
    .whenNew(PrintWriter.class)
    .withArguments(output)
    .thenReturn(writer);

但是我知道与这位作家没有任何互动。任何帮助将不胜感激。

Answer 1

如果您提供包含 PowerMock 配置的完整代码片段会更好。然后我可以帮助你并提供建议，现在我可能只能猜测可能出了什么问题，但我正在尝试：

PrintWriter有几个可以接受OutputStream的构造函数，而 PowerMock 有一个缺陷，当你只在类重载构造函数时传递参数时，它可能会错误地猜测哪个构造函数被模拟。

也可能是常见的错误，您没有添加创建PrintWriter实例的类来@PrepareForTest。

因此，基于我的假设案例的工作示例：

public class PrintWriterCreator {
    private final PrintWriter printWriter;
    public PrintWriterCreator(OutputStream outputStream) {
        this.printWriter = new PrintWriter(outputStream);
    }
    public void write(String message){
        printWriter.write(message);
    }
}

测试类：

@RunWith(PowerMockRunner.class)
@PrepareForTest({PrintWriter.class, PrintWriterCreator.class})
public class PrintWriterCreatorTest {

    @Mock
    private OutputStream outputStream;
    @Mock
    private PrintWriter printWriterMock;
    private PrintWriterCreator printWriterCreator;

    @Before
    public void setUp() throws Exception {
        whenNew(PrintWriter.class).withParameterTypes(OutputStream.class).withArguments(eq(outputStream)).thenReturn
                                                                                                       (printWriterMock);
        printWriterCreator = new PrintWriterCreator(outputStream);
    }
    @Test
    public void testWrite() throws Exception {
        String message = "someMessage";
        printWriterCreator.write(message);
        verifyNew(PrintWriter.class).withArguments(outputStream);
        verify(printWriterMock).write(eq(message));
    }

}