如何对hashCode()进行单元测试? [英] How can I do unit test for hashCode()?

问题描述

如何在单元测试中测试hashCode()函数?

How can I test the hashCode() function in unit testing?

public int hashCode(){
    int result = 17 + hashDouble(re);
    result = 31 * result + hashDouble(im);
    return result;
}

推荐答案

每当我覆盖equals和hash代码时，我都会按照Joshua Bloch在有效Java"第3章中的建议编写单元测试.是自反的，对称的和可传递的.我还确保不等于"对所有数据成员均正常工作.

Whenever I override equals and hash code, I write unit tests that follow Joshua Bloch's recommendations in "Effective Java" Chapter 3. I make sure that equals and hash code are reflexive, symmetric, and transitive. I also make sure that "not equals" works properly for all the data members.

当我检查对equals的调用时，我还要确保hashCode的行为符合预期.像这样:

When I check the call to equals, I also make sure that the hashCode behaves as it should. Like this:

@Test
public void testEquals_Symmetric() {
    Person x = new Person("Foo Bar");  // equals and hashCode check name field value
    Person y = new Person("Foo Bar");
    Assert.assertTrue(x.equals(y) && y.equals(x));
    Assert.assertTrue(x.hashCode() == y.hashCode());
}

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