JUnit 测试抛出异常的错误形式? [英] Bad form for JUnit test to throw exception?

问题描述

我对 JUnit 还很陌生，我真的不知道异常和异常处理的最佳实践是什么.

I'm pretty new to JUnit, and I don't really know what best practices are for exceptions and exception handling.

例如，假设我正在为 IPAddress 类编写测试.它有一个构造函数 IPAddress(String addr)，如果 addr 为 null，它将抛出 InvalidIPAddressException.据我通过谷歌搜索得知，空参数的测试将如下所示.

For example, let's say I'm writing tests for an IPAddress class. It has a constructor IPAddress(String addr) that will throw an InvalidIPAddressException if addr is null. As far as I can tell from googling around, the test for the null parameter will look like this.

@Test
public void testNullParameter()
{
    try
    {
        IPAddress addr = new IPAddress(null);
        assertTrue(addr.getOctets() == null);
    }
    catch(InvalidIPAddressException e)
    {
        return;
    }

    fail("InvalidIPAddressException not thrown.");
}

在这种情况下，try/catch 是有意义的，因为我知道异常即将到来.

In this case, try/catch makes sense because I know the exception is coming.

但是现在如果我想编写 testValidIPAddress()，有几种方法可以做到:

But now if I want to write testValidIPAddress(), there's a couple of ways to do it:

方式#1:

@Test
public void testValidIPAddress() throws InvalidIPAddressException
{
    IPAddress addr = new IPAddress("127.0.0.1");
    byte[] octets = addr.getOctets();

    assertTrue(octets[0] == 127);
    assertTrue(octets[1] == 0);
    assertTrue(octets[2] == 0);
    assertTrue(octets[3] == 1);
}

方式#2:

@Test
public void testValidIPAddress()
{
    try
    {
        IPAddress addr = new IPAddress("127.0.0.1");
        byte[] octets = addr.getOctets();

        assertTrue(octets[0] == 127);
        assertTrue(octets[1] == 0);
        assertTrue(octets[2] == 0);
        assertTrue(octets[3] == 1);
    }
    catch (InvalidIPAddressException e)
    {
        fail("InvalidIPAddressException: " + e.getMessage());
    }
}

标准做法是向 JUnit 抛出意外异常还是自己处理它们?

Is is standard practice to throw unexpected exceptions to JUnit or just deal with them yourself?

感谢您的帮助.

推荐答案

实际上，异常测试的旧风格是在抛出异常的代码周围包裹一个 try 块，然后添加一个 <代码>fail() 语句在 try 块的末尾.像这样:

Actually, the old style of exception testing is to wrap a try block around the code that throws the exception and then add a fail() statement at the end of the try block. Something like this:

public void testNullParameter() {
    try {
        IPAddress addr = new IPAddress(null);
        fail("InvalidIPAddressException not thrown.");
    } catch(InvalidIPAddressException e) {
        assertNotNull(e.getMessage());
    }
}

这和你写的没什么不同，但是:

This isn't much different from what you wrote but:

1. 你的assertTrue(addr.getOc​​tets() == null);没用.
2. IMO 的意图和语法更清晰，因此更易于阅读.

不过，这有点难看.但这正是 JUnit 4 的用武之地，因为异常测试是 JUnit 4 中最大的改进之一.使用 JUnit 4，您现在可以像这样编写测试:

Still, this is a bit ugly. But this is where JUnit 4 comes to the rescue as exception testing is one of the biggest improvements in JUnit 4. With JUnit 4, you can now write your test like this:

@Test (expected=InvalidIPAddressException.class) 
public void testNullParameter() throws InvalidIPAddressException {
    IPAddress addr = new IPAddress(null);
}

很好，不是吗?

现在，关于真正的问题，如果我不希望抛出异常，我肯定会选择方法 #1(因为它不那么冗长)并让 JUnit 处理异常并按预期失败测试.

Now, regarding the real question, if I don't expect an exception to be thrown, I'd definitely go for way #1 (because it's less verbose) and let JUnit handle the exception and fail the test as expected.

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