如何在Java中测试写入文件？

Question

我是初学者,掌握在手中.我有一些简单的程序,我需要对write方法进行junit测试.我在输入中有一些收藏.我怎么能这样做？这是我的代码:

// write to file
public void write(String fileName, 
        List<FigureGeneral> figuresList) {
    try {
        PrintWriter out = new PrintWriter(
                new File(fileName).getAbsoluteFile());
        try {
            for (int i = 0; i < figuresList.size(); i++) {
                out.println(figuresList.get(i).toString());
            }
        } finally {
            out.close();
        }
    } catch (IOException e) {
        System.out.println("Cannot write to file!");
    }
}

我想知道,因为我从文件中读取后,我们可以加入两个测试(写/读)或者更好地单独执行(如果我们的测试失败,我们不知道哪里有问题 - 读或写)？如何在junit上正确地做这个(准备测试,并测试自己)？更好地展示示例,这种方式更好地理解.

谢谢你,纳扎尔.

Answer 1

你可能根本不需要嘲笑.尝试在测试中使用StringWriter.

// write to file
public void write(String fileName, List<FigureGeneral> figuresList) {
  try {
    Writer out = new FileWriter(new File(fileName).getAbsoluteFile());
    write(out, figuresList);
  } catch (IOException e) {
    System.out.println("Cannot write to file!");
  }
}

@VisibleForTesting void write(Writer writer, List<FigureGeneral> figuresList) {
  PrintWriter out = new PrintWriter(writer);
  try {
    for (int i = 0; i < figuresList.size(); i++) {
      out.println(figuresList.get(i).toString());
    }
  } finally {
    out.close();
  }
}

@Test public void testWrite() {
  List<FigureGeneral> list = Lists.newArrayList();
  list.add(...); // A
  list.add(...); // B
  list.add(...); // C
  StringWriter stringWriter = new StringWriter();
  write(stringWriter, list);
  assertEquals("A.\nB.\nC.\n", stringWriter.toString()); 
}

Answer 2

我建议你在你的IO类(PrintWriter你的情况下是类)中创建一个接口包装器,这样你就可以使用模拟对象来输出.你不必测试Java PrintWriter,你想测试你的功能,对吗？

所以你的课程将是

class MyClass {

    MyWriter out;

    public void setOut(MyWriter out) {
        this.out = out;
    }

    // write to file
    public void write(String fileName, List<FigureGeneral> figuresList) {
        try {
            try {
                for (int i = 0; i < figuresList.size(); i++) {
                    out.println(figuresList.get(i).toString());
                }
            } finally {
                out.close();
            }
        } catch (IOException e) {
            System.out.println("Cannot write to file!");
        }
    }
}

MyWriter界面的签名非常简单.

interface MyWriter {

    void println(Object x); // You can add other println methods here.

    void close();

}

然后,您可以使用EasyMock编写测试.测试方法就像是

@Test
public void testWrite() {
    MyWriter out = EasyMock.createMock(MyWriter.class);
    EasyMock.expect(mock.println(EasyMock.anyObject())).times(3);
    EasyMock.expect(mock.close()).times(1);

    List<FigureGeneral> list = ...
    list.add(...);
    list.add(...);
    list.add(...);

    replay(mock);

    MyClass myClass = new MyClass();
    myClass.setOut(out);
    myClass.write("mockFileName", list);        

    verify(mock);
}