如何为 FileWriter 运行 Junit 测试用例？

Question

下面的代码是将内容写入到文件中。

          public String saveSecretToFile() {
            File file = new File("test.txt");
            try (BufferedWriter writer = new BufferedWriter(new FileWriter(file))) {
                writer.write(secretValue);//secretValue is the content
            } catch (IOException e) {
                LOGGER.error("Error writing to file: {}", e.getMessage());
            }
          }

JUnit 测试用例中未涵盖 catch 块。

    @InjectMocks
    private MyHelper myHelper;

        try (MockedStatic<FileOutputStream> mockedStatic = Mockito.mockStatic(FileOutputStream.class)) {
            FileWriter mockFile = mock(FileWriter.class);
            OutputStream mockFileWriter = Mockito.spy(new FileOutputStream(String.valueOf(mockFile)));
            
            doThrow(new IOException("IO error")).when(mockFileWriter).write(anyString().getBytes());
            
            IOException thrown = assertThrows(IOException.class, () -> myHelper.saveToFile("secretName"));  
            
        }

我读过，模拟 BufferedWriter 不起作用，因为应该模拟 FileWriter 的内部 OutputStream。 unitest 情况的预期结果是抛出异常。但是，结果显示为 java.lang.AssertionError：预期抛出 java.io.IOException，但没有抛出任何内容

Answer 1

我会做这样的事情：

1- 首先实现写入模拟。

public class MyHelper {
    private final BufferedWriter writer;

    // Constructor for dependency injection
    public MyHelper(BufferedWriter writer) {
        this.writer = writer;
    }

    public void saveSecretToFile(String secretValue) {
        try {
            writer.write(secretValue);
            writer.flush();
        } catch (IOException e) {
            LOGGER.error("Error writing to file: {}", e.getMessage());
            throw new RuntimeException("Error writing to file", e); // Throw to signify error
        }
    }
}

2- 使用我以前的服务的模拟，使用 IOException 将测试写入快乐路径和不快乐路径，并检查该方法是否被调用。

有一个验证检查该方法是否已被调用。

import static org.mockito.Mockito.*;
import static org.junit.jupiter.api.Assertions.*;

import java.io.BufferedWriter;
import java.io.IOException;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.mockito.*;

class MyHelperTest {
    @Mock
    private BufferedWriter mockWriter;

    @InjectMocks
    private MyHelper myHelper;

    @BeforeEach
    void setUp() {
        MockitoAnnotations.openMocks(this);
    }

    @Test
    void testSaveSecretToFile_Success() throws IOException {
        // Arrange
        String secretValue = "secret";

        // Act
        myHelper.saveSecretToFile(secretValue);

        // Assert
        verify(mockWriter, times(1)).write(secretValue);
        verify(mockWriter, times(1)).flush();
    }

    @Test
    void testSaveSecretToFile_ThrowsException() throws IOException {
        // Arrange
        String secretValue = "secret";
        doThrow(new IOException("IO error")).when(mockWriter).write(anyString());

        // Act & Assert
        Exception exception = assertThrows(RuntimeException.class, () -> myHelper.saveSecretToFile(secretValue));
        assertTrue(exception.getCause() instanceof IOException);
        assertEquals("Error writing to file", exception.getMessage());
        verify(mockWriter, times(1)).write(secretValue); // Verify write was called before exception
    }
}