比较器的Junit Matcher？

Question

这几天我都在使用 Junit 的 Matchers 功能。一切正常，但我正在寻找一个匹配器，它使用比较器进行比较并且不依赖对象 equals 方法。

我要换

Assert.assertThat(one, CoreMatchers.equalTo(two)

类似（伪代码）

Assert.assertThat(eins, CoreMatchers.equalTo(operand, new MyComparator())

您知道是否存在简单的开箱即用解决方案？我在 google 中没有找到，也不想写一篇。

Answer 1

Hamcrest 2.0.0.0+ 现在支持此功能。

您可以使用org.hamcrest.comparator.ComparatorMatcherBuilder 类来实现这一点，例如：

ComparatorMatcherBuilder builder = ComparatorMatcherBuilder.comparedBy(equivalenceComparator);
Assert.assertThat(eins, builder.comparesEqualTo(operand));

Answer 2

我在 hamcrest 1.3 中遇到了同样的问题，并通过编写一个匹配器来解决它，它遵循 IsEqual-Matcher 的代码，但使用给定的比较器而不是 Object#equals()。

import org.hamcrest.BaseMatcher;
import org.hamcrest.Description;
import org.hamcrest.Factory;
import org.hamcrest.Matcher;
import org.junit.Assert;

import java.lang.reflect.Array;
import java.util.Comparator;

/**
 * Is the value equal to another value, as tested by the
 * given Comparator?<br/>
 * Based on the example of {@link org.hamcrest.core.IsEqual}.
 *
 * @author Serhat Cinar
 */
public class IsEqualWithComparator<T> extends BaseMatcher<T> {
    private final Object expectedValue;
    private final Comparator<T> comparator;

    public IsEqualWithComparator(T equalArg, Comparator<T> comparator) {
        expectedValue = equalArg;
        this.comparator = comparator;
    }

    @Override
    public boolean matches(Object actualValue) {
        return areEqual(actualValue, expectedValue, comparator);
    }

    @Override
    public void describeTo(Description description) {
        description.appendValue(expectedValue);
    }

    private static boolean areEqual(Object actual, Object expected, Comparator comparator) {
        if (actual == null) {
            return expected == null;
        }

        if (expected != null && isArray(actual)) {
            return isArray(expected) && areArraysEqual(actual, expected, comparator);
        }

        return comparator.compare(actual, expected) == 0;
    }

    private static boolean areArraysEqual(Object actualArray, Object expectedArray, Comparator comparator) {
        return areArrayLengthsEqual(actualArray, expectedArray) && areArrayElementsEqual(actualArray, expectedArray, comparator);
    }

    private static boolean areArrayLengthsEqual(Object actualArray, Object expectedArray) {
        return Array.getLength(actualArray) == Array.getLength(expectedArray);
    }

    private static boolean areArrayElementsEqual(Object actualArray, Object expectedArray, Comparator comparator) {
        for (int i = 0; i < Array.getLength(actualArray); i++) {
            if (!areEqual(Array.get(actualArray, i), Array.get(expectedArray, i), comparator)) {
                return false;
            }
        }
        return true;
    }

    private static boolean isArray(Object o) {
        return o.getClass().isArray();
    }

    @Factory
    public static <T> Matcher<T> equalTo(T operand, Comparator<T> comparator) {
        return new IsEqualWithComparator<>(operand, comparator);
    }

    public static void main(String argv[]) {
        Assert.assertThat("abc", IsEqualWithComparator.equalTo("ABC", new Comparator<String>() {
            @Override
            public int compare(String o1, String o2) {
                return o1.equalsIgnoreCase(o2) ? 0 : -1;
            }
        }));
    }
}

Answer 3

另一种选择是将AspectJ framework custom comparison strategy 用于对象和可迭代对象。

assertThat(frodo).usingComparator(raceComparator).isEqualTo(sam);
assertThat(fellowshipOfTheRing).usingElementComparator(raceComparator).contains(sauron);

它也有Field by field comparisons，例如isEqualToComparingOnlyGivenFields 和 isEqualToIgnoringGivenFields 比较器。

assertThat(frodo).isEqualToComparingOnlyGivenFields(sam, "race.name");
assertThat(frodo).isEqualToIgnoringGivenFields(sam, "name", "age");

因此，在大多数情况下，您可以在没有自定义比较策略的情况下处理断言

Answer 4

我不知道 Hamcrest 有什么东西可以做到这一点。您可能需要编写自定义匹配器。需要考虑的一件事：如果equals 没有返回true，对象是否相等？如果您正在测试特定属性，您的自定义匹配器可能会更清晰地显示为FeatureMatcher (Is there a simple way to match a field using Hamcrest?)。例如，如果测试是针对预期标签的：

assertThat(eins, equalToUnderComparison("1", new LabelComparator());

可能更清楚：

assertThat(eins, hasLabel(eq("1")));

编写自定义匹配器不需要大量代码 (Writing custom matchers)，如果它使代码更具可读性，就没有理由避免它。