java - 如何在 JUnit 中测试 void 方法

Question

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Answer 1

如果方法有副作用，您可以在 JUnit 测试中检查它们。

在您的示例中，该方法没有副作用，因此无需测试。

如果你还想测试它，你可以使用反射来这样做，但我认为这不是一个好的做法。

可以查看JUnit FAQ相关部分:

How do I test a method that doesn't return anything?

Often if a method doesn't return a value, it will have some side effect. Actually, if it doesn't return a value AND doesn't have a side effect, it isn't doing anything.

There may be a way to verify that the side effect actually occurred as expected. For example, consider the add() method in the Collection classes. There are ways of verifying that the side effect happened (i.e. the object was added). You can check the size and assert that it is what is expected:

@Test
public void testCollectionAdd() {
    Collection collection = new ArrayList();
    assertEquals(0, collection.size());
    collection.add("itemA");
    assertEquals(1, collection.size());
    collection.add("itemB");
    assertEquals(2, collection.size());
}

Another approach is to make use of MockObjects.

A related issue is to design for testing. For example, if you have a method that is meant to output to a file, don't pass in a filename, or even a FileWriter. Instead, pass in a Writer. That way you can pass in a StringWriter to capture the output for testing purposes. Then you can add a method (e.g. writeToFileNamed(String filename)) to encapsulate the FileWriter creation.