管理检查 JUnit 中抛出的 ExpectedException 的规则

Question

我的任务是计算给定的两个字符串中不匹配（不同字符）的数量。虽然;有两个条件需要满足。

If the lengths of given two Strings are not same; throw an Exception with appropriate message.

If only one input String is provided; throw an Exception with appropriate message.

我的解决方案：

class Hamming {
    private final String leftString;
    private final String rightString;

    public Hamming(String leftString, String rightString) {
        this.leftString = leftString;
        this.rightString = rightString;
    }

    public int getHammingDistance() {
        int hammingDistance = 0;
        int secondCharIndex = 0;
        if (leftString.length() == 0 && rightString.length() != 0)
            throw new IllegalArgumentException("left string must not be empty.");
        if (rightString.length() == 0 && leftString.length() != 0)
            throw new IllegalArgumentException("right string must not be empty.");
        if (leftString.length() != rightString.length())
            throw new IllegalArgumentException("left and right string must be of equal length.");
        for (char ch : leftString.toCharArray()) {
            if (ch != rightString.charAt(secondCharIndex)) hammingDistance++;
            secondCharIndex++;
        }
        return hammingDistance;
    }
}

现在，当我运行直接使用这个解决方案时；它按预期工作。您可以找到上述代码的运行示例 here.

当我尝试运行使用 Junit 测试覆盖率 的相同代码时；相同的代码无法通过所有涉及异常的测试用例。下面是我的 HammingTest.java

import static org.assertj.core.api.Assertions.assertThat;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertThrows;

import org.junit.Ignore;
import org.junit.Test;

public class HammingTest {

    @Test
    public void testNoDistanceBetweenEmptyStrings() {
        assertEquals(0, new Hamming("", "").getHammingDistance());
    }

//    @Ignore("Remove to run test")
    @Test
    public void testNoDistanceBetweenShortIdenticalStrings() {
        assertEquals(0, new Hamming("A", "A").getHammingDistance());
    }

//    @Ignore("Remove to run test")
    @Test
    public void testCompleteDistanceInSingleLetterDifferentStrings() {
        assertEquals(1, new Hamming("G", "T").getHammingDistance());
    }

//    @Ignore("Remove to run test")
    @Test
    public void testDistanceInLongIdenticalStrings() {
        assertEquals(0, new Hamming("GGACTGAAATCTG", "GGACTGAAATCTG").getHammingDistance());
    }

//    @Ignore("Remove to run test")
    @Test
    public void testDistanceInLongDifferentStrings() {
        assertEquals(9, new Hamming("GGACGGATTCTG", "AGGACGGATTCT").getHammingDistance());
    }

//    @Ignore("Remove to run test")
    @Test
    public void testValidatesFirstStringNotLonger() {
        IllegalArgumentException expected =
            assertThrows(
                IllegalArgumentException.class,
                () -> new Hamming("AATG", "AAA"));

        assertThat(expected)
            .hasMessage("left and right string must be of equal length.");
    }

//    @Ignore("Remove to run test")
    @Test
    public void testValidatesSecondStringNotLonger() {
        IllegalArgumentException expected =
            assertThrows(
                IllegalArgumentException.class,
                () -> new Hamming("ATA", "AGTG"));

        assertThat(expected)
            .hasMessage("left and right string must be of equal length.");
    }

//    @Ignore("Remove to run test")
    @Test
    public void testDisallowLeftEmptyString() {
        IllegalArgumentException expected =
            assertThrows(
                IllegalArgumentException.class,
                () -> new Hamming("", "G"));

        assertThat(expected)
            .hasMessage("left string must not be empty.");
    }

//    @Ignore("Remove to run test")
    @Test
    public void testDisallowRightEmptyString() {
        IllegalArgumentException expected =
            assertThrows(
                IllegalArgumentException.class,
                () -> new Hamming("G", ""));

        assertThat(expected)
            .hasMessage("right string must not be empty.");
    }

}

我将该项目用作 gradle 项目。 因此生成的报告显示了以下问题：

是什么解决了我的问题：

工作久了；当我最终尝试 将异常抛出条件放入 Constructor 时；它解决了我的问题。每个测试用例都通过了。像这样的东西：

public Hamming(String leftString, String rightString) {
        if (leftString.length() == 0 && rightString.length() != 0) {
            throw new IllegalArgumentException("left string must not be empty.");
        } else if (rightString.length() == 0 && leftString.length() != 0) {
            throw new IllegalArgumentException("right string must not be empty.");
        } else if (leftString.length() != rightString.length()) {
            throw new IllegalArgumentException("leftString and rightString must be of equal length.");
        }
        this.leftSting = leftString;
        this.rightString = rightString;
    }

我的疑惑是什么：

为什么将异常抛出条件放在构造函数中的解决方案有效？
当我试图将异常抛出条件放入 getHamming() 方法时；为什么测试失败了？
当我运行使用前面提到的相同 Hamming class 而没有使用 JUnit 时；它按预期工作。为什么会这样？

任何帮助都会有所帮助。

Answer 1

您错过了 getHammingDistance() 电话，这就是您的测试用例失败的原因。让我们来一个测试用例，看看为什么。

@Test
public void testValidatesFirstStringNotLonger() {
    IllegalArgumentException expected =
        assertThrows(
            IllegalArgumentException.class,
            () -> new Hamming("AATG", "AAA"));

    assertThat(expected)
        .hasMessage("left and right string must be of equal length.");
}

第一个 assertThrows 检查 new Hamming("AATG", "AAA") 是否因 IllegalArgumentException 而失败。由于异常是在方法 getHammingDistance() 中引发的，因此断言失败。

这会奏效：

@Test
public void testValidatesFirstStringNotLonger() {
    Hamming hamming = new Hamming("AATG", "AAA");

    IllegalArgumentException expected =
        assertThrows(
            IllegalArgumentException.class,
            () -> hamming.getHammingDistance());

    assertThat(expected)
        .hasMessage("left and right string must be of equal length.");
}

管理检查 JUnit 中抛出的 ExpectedException 的规则

Rules that govern Checking for ExpectedException thrown in JUnit

java

unit-testing

exception

junit4

gradle