java - 如何测试这个文件写入，3lines 功能？

Question

这是我在某个服务类中的方法。它是公开的，因此应该对其进行测试。我根本不知道我应该测试什么。我会模拟 Writer 和 spyOn 函数调用，但使用此实现是不可能的(不是吗？)

我正在使用 Mockito 和 JUnit

目前，我只能创建抛出异常并断言该异常的函数

有什么帮助吗？

@Override
public void initIndexFile(File emptyIndexFile) {
    try {
        Writer writer = new FileWriter(emptyIndexFile);
        writer.write("[]");
        writer.close();
    } catch (IOException e) {
        throw new IndexFileInitializationException(
            "Error initialization index file " + emptyIndexFile.getPath()
        );
    }
}

Answer 1

如果您认为添加特殊内容是业务逻辑，因此是您类的责任，那么创建 FileWriter 不是(根据 >单一职责模式。

因此，您应该使用一个 FileWriterFactory，它被注入(inject)到您的被测类中。然后您可以模拟 FileWriterFactory 以返回 Writer 接口(interface)的模拟实现，然后您可以在该接口(interface)上检查它是否获得了预期的字符串。

你的 CuT 会变成这样:

private final WriterFactory writerFactory;

public ClassUnderTest(@Inject WriterFactory writerFactory){
   this.writerFactory = writerFactory;
}

@Override
public void initIndexFile(File emptyIndexFile) {
    try {
        Writer writer = writerFactory.create(emptyIndexFile);
        writer.write("[]");
        writer.close();
    } catch (IOException e) {
        throw new IndexFileInitializationException(
            "Error initialization index file " + emptyIndexFile.getPath()
        );
    }
}

和你对此的测试:

class Test{

  @Rule public MockitoRule mockitoRule = MockitoJUnit.rule(); 

  @Mock
  private FileWriterFactory fileWriterFactory;
  private Writer fileWriter = spy(new StringWriter());
  File anyValidFile = new File(".");
  @Test
  public void initIndexFile_validFile_addsEmptyraces(){
     //arrange
     doReturn(fileWriter).when(fileWriterFactory).create(any(File.class));

     // act
     new ClassUnderTest(fileWriterFactory).initIndexFile(anyValidFile);

     //assert
     verify(fileWriterFactory)create(anyValidFile);
     assertEquals("text written to File", "[]", fileWriter.toString());
     verify(fileWriter).close();
  }
}

此外，您可以轻松地检查您的 CuT 是否拦截了 IOException:

  @Rule
  public ExpectedException exception = ExpectedException.none();

  @Test
  public void initIndexFile_missingFile_IndexFileInitializationException(){
     //arrange
     doReturnThrow(new IOException("UnitTest")).when(fileWriterFactory).create(any(File.class));

     //assert
     exception.expect(IndexFileInitializationException.class);
     exception.expectMessage("Error initialization index file "+anyValidFile.getPath());

     // act
     new ClassUnderTest(fileWriterFactory).initIndexFile(anyValidFile);
  }

---

Nice! a factory just to test 3 lines of code! – Nicolas Filotto

这是一个很好的观点。

问题是:该类中是否有任何方法直接与 File 对象交互并且之后需要创建 FileWriter？

如果根据 KISS 原则答案是“否”(这很可能是这样)，您应该直接注入(inject)一个 Writer 对象而不是工厂，并且您的方法不带 File 参数。

private final Writer writer;

public ClassUnderTest(@Inject Writer writer){
   this.writer = writer;
}

@Override
public void initIndexFile() {
    try {
        writer.write("[]");
        writer.close();
    } catch (IOException e) {
        throw new IndexFileInitializationException(
            "Error initialization index file " + emptyIndexFile.getPath()
        );
    }
}

修改后的测试:

class Test{       
  @Rule public MockitoRule mockitoRule = MockitoJUnit.rule(); 
  @Rule public ExpectedException exception = ExpectedException.none();

  @Mock
  private FileWriterFactory fileWriterFactory;
  @Mock
  private Writer failingFileWriter;
  private Writer validFileWriter = spy(new StringWriter());
  File anyValidFile = new File(".");
  @Test
  public void initIndexFile_validFile_addsEmptyraces(){
     //arrange         
     // act
     new ClassUnderTest(validFileWriter).initIndexFile();

     //assert
     verify(fileWriterFactory)create(anyValidFile);
     assertEquals("text written to File", "[]", fileWriter.toString());
     verify(fileWriter).close();
  }

  @Test
  public void initIndexFile_missingFile_IndexFileInitializationException(){
     //arrange
     doReturnThrow(new IOException("UnitTest")).when(failingFileWriter).write(anyString());

     //assert
     exception.expect(IndexFileInitializationException.class);
     exception.expectMessage("Error initialization index file "+anyValidFile.getPath());

     // act
     new ClassUnderTest(fileWriterFactory).initIndexFile(anyValidFile);
  }
}