hashCode/equals 合约的 JUnit 理论 [英] JUnit theory for hashCode/equals contract

问题描述

以下类用作 equals/hashCode 合同的通用测试器.它是本土测试框架的一部分.

The following class serve as generic tester for equals/hashCode contract. It is a part of a home grown testing framework.

• 你在想什么?
• 我如何(强)测试这门课?
• 这是对 Junit 理论的一个很好的利用吗?

班级:

@Ignore
@RunWith(Theories.class)
public abstract class ObjectTest {

    // For any non-null reference value x, x.equals(x) should return true
    @Theory
    public void equalsIsReflexive(Object x) {
        assumeThat(x, is(not(equalTo(null))));
        assertThat(x.equals(x), is(true));
    }

    // For any non-null reference values x and y, x.equals(y) 
    // should return true if and only if y.equals(x) returns true.
    @Theory
    public void equalsIsSymmetric(Object x, Object y) {
        assumeThat(x, is(not(equalTo(null))));
        assumeThat(y, is(not(equalTo(null))));
        assumeThat(y.equals(x), is(true));
        assertThat(x.equals(y), is(true));
    }

    // For any non-null reference values x, y, and z, if x.equals(y)
    // returns true and y.equals(z) returns true, then x.equals(z) 
    // should return true.
    @Theory
    public void equalsIsTransitive(Object x, Object y, Object z) {
        assumeThat(x, is(not(equalTo(null))));
        assumeThat(y, is(not(equalTo(null))));
        assumeThat(z, is(not(equalTo(null))));
        assumeThat(x.equals(y) && y.equals(z), is(true));
        assertThat(z.equals(x), is(true));
    }

    // For any non-null reference values x and y, multiple invocations
    // of x.equals(y) consistently return true  or consistently return
    // false, provided no information used in equals comparisons on
    // the objects is modified.
    @Theory
    public void equalsIsConsistent(Object x, Object y) {
        assumeThat(x, is(not(equalTo(null))));
        boolean alwaysTheSame = x.equals(y);

        for (int i = 0; i < 30; i++) {
            assertThat(x.equals(y), is(alwaysTheSame));
        }
    }

    // For any non-null reference value x, x.equals(null) should
    // return false.
    @Theory
    public void equalsReturnFalseOnNull(Object x) {
        assumeThat(x, is(not(equalTo(null))));
        assertThat(x.equals(null), is(false));
    }

    // Whenever it is invoked on the same object more than once 
    // the hashCode() method must consistently return the same 
    // integer.
    @Theory
    public void hashCodeIsSelfConsistent(Object x) {
        assumeThat(x, is(not(equalTo(null))));
        int alwaysTheSame = x.hashCode();

        for (int i = 0; i < 30; i++) {
            assertThat(x.hashCode(), is(alwaysTheSame));
        }
    }

    // If two objects are equal according to the equals(Object) method,
    // then calling the hashCode method on each of the two objects
    // must produce the same integer result.
    @Theory
    public void hashCodeIsConsistentWithEquals(Object x, Object y) {
        assumeThat(x, is(not(equalTo(null))));
        assumeThat(x.equals(y), is(true));
        assertThat(x.hashCode(), is(equalTo(y.hashCode())));
    }

    // Test that x.equals(y) where x and y are the same datapoint 
    // instance works. User must provide datapoints that are not equal.
    @Theory
    public void equalsWorks(Object x, Object y) {
        assumeThat(x, is(not(equalTo(null))));
        assumeThat(x == y, is(true));
        assertThat(x.equals(y), is(true));
    }

    // Test that x.equals(y) where x and y are the same datapoint instance
    // works. User must provide datapoints that are not equal.
    @Theory
    public void notEqualsWorks(Object x, Object y) {
        assumeThat(x, is(not(equalTo(null))));
        assumeThat(x != y, is(true));
        assertThat(x.equals(y), is(false));
    }
}

用法:

import org.junit.experimental.theories.DataPoint;

public class ObjectTestTest extends ObjectTest {

    @DataPoint
    public static String a = "a";
    @DataPoint
    public static String b = "b";
    @DataPoint
    public static String nullString = null;
    @DataPoint
    public static String emptyString = "";
}

推荐答案

需要考虑的一件事:测试对象是否符合 equals 约定应该涉及其他类型的实例.特别是，子类或超类的实例可能会出现问题.Joshua Bloch 在Effective Java (I正在重复使用 duffymo 的链接，因此他应该为此获得赞誉)——请参阅涉及 Point 和 ColorPoint 类的 Transitivity 下的部分.

One thing to consider: testing an object's conformance to the equals contract should involve instances of other types. In particular, problems are likely to appear with instances of a subclass or superclass. Joshua Bloch gives an excellent explanation of the related pitfalls in Effective Java (I'm reusing duffymo's link, so he should get credit for it) -- see the section under Transitivity involving the Point and ColorPoint classes.

确实，您的实现不会阻止某人编写涉及子类实例的测试，但是由于 ObjectTest 是一个通用类，它给人的印象是所有数据点都应该来自单个类(被测试的类).完全删除类型参数可能会更好.仅供参考.

True, your implementation doesn't prevent someone from writing a test that involves instances of a subclass, but because ObjectTest is a generic class it gives the impression that all data points should come from a single class (the class being tested). It might be better to remove the type parameter altogether. Just food for thought.

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