java - 已具有 try-catch 子句的方法的 Junit 测试用例

Question

我正在尝试为 ErParser 类中的 setTrailer() 方法编写一个测试用例。 setTrailer() 具有 try-catch 子句，并且在其中一个 catch 子句中，它捕获 NullPointerException。我正在尝试为 setTrailer() 抛出并捕获 NullPointerException 的情况编写 Junit 测试，但测试用例始终失败。是因为我已经在方法本身中捕获了异常吗？我应该在测试用例中捕获异常吗？

测试用例:

public class TestERParser { 
    @Test(expected=NullPointerException.class)
    public void nullSetTrailer() {
        ERParser recCurrParse = new ERParser();
        recCurrParse.setTrailer(null);
    }   
}

ERParser 类中的 setTrailer() 方法:

public class ERParser {
private static final String TRAILER_E = "GRAND TOTAL";
private static final String TRAILER_R = "TRAILER";
public String trailerRecord; 

/**
 * Constructs an ERParser object.
 */
public ERParser() {
    this.trailerRecord = null;
    this.trailerVals = null;
}
/**
 * Populates the trailerRecord field with the summary (trailer) record of the input file.
 * @param file  Input file
 * @throws NullPointerException, FileNotFoundException, IOException
 */
public void setTrailer(File file) {
    try {
        FileReader fReader = new FileReader(file);
        BufferedReader bReader = new BufferedReader (fReader);
        String currLine = new String();
        readLoop:
            while (bReader.ready()) {
                currLine = bReader.readLine();
                if (currLine.contains(TRAILER_E) || currLine.contains(TRAILER_R)) {
                    break readLoop;
                }
            }
        this.trailerRecord = currLine.trim();
        System.out.println("From setTrailer(): " + this.trailerRecord);
        fReader.close();
        bReader.close();
    } catch (NullPointerException exception) {
        exception.printStackTrace();
    } catch (FileNotFoundException exception) {
        exception.printStackTrace();
    } catch (IOException exception) {
        exception.printStackTrace();
    }
}
}

Answer 1

正如您怀疑的那样，您在代码中捕获了 NPE，并且它没有被传播。如果您希望用户捕获此异常，您应该删除此代码并用 throws 装饰您的方法到适当的类。

public void setTrailer(File file) throws Exception {
        FileReader fReader = new FileReader(file);
        BufferedReader bReader = new BufferedReader (fReader);
        String currLine = new String();
        readLoop:
            while (bReader.ready()) {
                currLine = bReader.readLine();
                if (currLine.contains(TRAILER_E) || currLine.contains(TRAILER_R)) {
                    break readLoop;
                }
            }
        this.trailerRecord = currLine.trim();
        System.out.println("From setTrailer(): " + this.trailerRecord);
        fReader.close();
        bReader.close();
}

由于您的代码现在抛出已检查的异常，因此您需要稍微更新您的 Junit 方法，以捕获已检查的异常

   @Test(expected=NullPointerException.class)
    public void nullSetTrailer() throws Exception {
        ERParser recCurrParse = new ERParser();
        recCurrParse.setTrailer(null);
    }