在一个单元测试中有多个断言是不好的做法吗? [英] Is it bad practice to have more than one assertion in a unit test?

问题描述

在单元测试中包含多个断言是一种不好的做法吗?有关系吗?

Is it bad practice to have more than one assertion in a unit test? Does it matter?

推荐答案

有时候，每个测试用例只有一个assert，但是我想更多的时候我有几个assert语句.

Sometimes I have exactly one assert per test case, but I think more often I have several assert statements.

我已经看到了@Arkain所遇到的情况，其中很大一部分代码只有一个单元测试套件，只有几个测试用例，它们都标记为testCase1，testCase2等，每个测试用例都有数百个断言.更好的是，每个条件通常取决于先前执行的副作用.每当构建失败时(总是在这样的单元测试中)，确定问题出在哪里都会花费相当多的时间.

I've seen the case that @Arkain eludes to, where a very large piece of code has a single unit test suite with just a few test cases, and they are all labeled testCase1, testCase2, etc, and each test case has hundreds of asserts. And even better, each condition usually depends upon the side-effects of previous execution. Whenever the build fails, invariably in such a unit test, it takes quite some time to determine where the problem was.

但是另一个极端是您的问题提出了什么:针对每种可能情况的单独测试用例.根据您要测试的内容，这可能是有道理的，但通常每个测试用例都有几个assert.

But the other extreme is what your question suggests: a separate test case for each possible condition. Depending on what you're testing, this might make sense, but often I have several asserts per test case.

例如，如果您编写了java.lang.Integer，则可能会遇到以下情况:

For instance, if you wrote java.lang.Integer, you might have some cases that look like:

public void testValueOf() {
    assertEquals(1, Integer.valueOf("1").intValue());
    assertEquals(0, Integer.valueOf("0").intValue());
    assertEquals(-1, Integer.valueOf("-1").intValue());
    assertEquals(Integer.MAX_VALUE, Integer.valueOf("2147483647").intValue());
    assertEquals(Integer.MIN_VALUE, Integer.valueOf("-2147483648").intValue());
    ....
}

public void testValueOfRange() {
    assertNumberFormatException("2147483648");
    assertNumberFormatException("-2147483649");
    ...
}

public void testValueOfNotNumbers() {
    assertNumberFormatException("");
    assertNumberFormatException("notanumber");
    ...
}
private void assertNumberFormatException(String numstr) {
    try {
        int number = Integer.valueOf(numstr).intValue();
        fail("Expected NumberFormatException for string \"" + numstr +
             "\" but instead got the number " + number);
    } catch(NumberFormatException e) {
        // expected exception
    }
}

对于要放入测试用例中的多个断言，我可以考虑一些简单的规则:

Some simple rules that I can think of off hand for how many assert's to put in a test case:

• 没有多少个assert取决于先前执行的副作用.
• 组assert一起测试相同的功能/特征或方面-不需要时不需要多个单元测试用例的开销.
• 以上任何规则均应被实用性和常识所取代.您可能不希望一千个单元测试用例中每个都有一个断言(甚至几个断言)，并且您不想要一个包含数百个assert语句的测试用例.

• Don't have more than one assert that depends on the side-effects of previous execution.
• Group asserts together that test the same function/feature or facet thereof--no need for the overhead of multiple unit test cases when it's not necessary.
• Any of the above rules should be overridden by practicality and common sense. You probably don't want a thousand unit test cases with a single assert in each (or even several asserts) and you don't want a single test case with hundreds of assert statements.

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