Hamcrest 测试匹配框架

短命女 2023-10-10 12:28 35阅读 0赞

## 为什么要用Hamcrest匹配器框架 ##

Hamcrest是一款软件测试框架, 可以通过现有的匹配器类检查代码中的条件.也可以通过自定义的匹配器实现.

要在JUnit中使用Hamcrest匹配器,可以用它的assertThat语句,并且可添加一个或多个匹配器.

Hamcrest一般被视作第三代匹配器框架.第一代使用断言(逻辑语句),但这样的测试不易读.第二代测试框架引入了特殊的断言方法,例如assertEquals().然而这种方式会导致编写过多类似的断言方法.Hamcrest采用了assertThat方法和匹配器表达式来确定测试是否成功,解决上述两个缺点.

Hamcrest的目标是使测试尽可能的提高可读性.例如is()方法其实就是equalTo()的包装方法

### 案例： ###

下面的代码就是一个使用Hamcrest

package com.lulu.androidtestdemo.hamcrest;
    import org.junit.Test;
    import static org.junit.Assert.assertEquals;
    import static org.hamcrest.MatcherAssert.assertThat;
    import static org.hamcrest.Matchers.*;
    
    /**
     * Created by lulu on 2018/3/17.
     */
    public class TestHamcrest {
        boolean a;
        boolean b;
        @Test
        public void testHamcrest() throws Exception {
            //下面语句的测试目的是一致的
            assertThat(a, equalTo(b));
            assertThat(a, is(equalTo(b)));
            assertThat(a, is(b));
        }
    }

下面代码比较了一下pure JUnit 4和使用Hamcrest的断言语句.

// JUnit 4 for equals check
    assertEquals(expected, actual);
    // Hamcrest for equals check
    assertThat(actual, is(equalTo(expected)));
    
    // JUnit 4 for not equals check
    assertNotEquals(expected, actual);
    // Hamcrest for not equals check
    assertThat(actual, is(not(equalTo(expected))));

也可以通过anyOf()等方法实现匹配器的链接.

assertThat("test", anyOf(is("testing"), containsString("est")));

通常Hamcrest的错误信息也更容易阅读.(下图为Pure JUnit 4和Hamcrest错误log的对比)

assertTrue(result instanceof String);
    // error message:
    java.lang.AssertionError
        at org.junit.Assert.fail(Assert.java:86)
        at org.junit.Assert.assertTrue(Assert.java:41)
        at org.junit.Assert.assertTrue(Assert.java:52)
    // ...
    
    
    assertEquals(String.class, result.getClass());
    // error message:
    java.lang.NullPointerException
        at com.vogella.hamcrest.HamcrestTest.test(HamcrestTest.java:30)
    // ....
    
    
    assertThat(result, instanceOf(String.class));
    // error message:
    java.lang.AssertionError:
    Expected: an instance of java.lang.String
         but: null
        at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
        at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:8)
    // ...

### 添加Hamcrest依赖 ###

<dependency>
    			<groupId>org.hamcrest</groupId>
    			<artifactId>hamcrest-core</artifactId>
    			<version>1.3</version>
    			<scope>test</scope>
    		</dependency>
    
    		<dependency>
    			<groupId>org.hamcrest</groupId>
    			<artifactId>hamcrest-library</artifactId>
    			<version>1.3</version>
    			<scope>test</scope>
    		</dependency>

### 使用Hamcrest ###

#### 示例： ####

Hamcrest匹配器的示例如下所示

assertThat(Long.valueOf(1), instanceOf(Integer.class));
    // shortcut for instanceOf
    assertThat(Long.valueOf(1), isA(Integer.class));

#### 静态导入 ####

使用静态导入可以使得所有匹配器都可用,更方便开发人员找到合适的匹配器.

import static org.hamcrest.MatcherAssert.assertThat;
    import static org.hamcrest.Matchers.*;

#### 一些重要的Hamcrest匹配器 ####

下面是一些非常重要且常用的Hamcrest匹配器

*  allOf - 所有匹配条件都匹配则通过
 *  anyOf - 任何一个匹配条件匹配则通过
 *  not - 与匹配条件违背则通过
 *  equalTo - 使用Object.equals方法测试对象相等
 *  is - 与equalTo相同,仅用来提高代码可读性
 *  hasToString - 测试 Object.toString方法
 *  instanceOf,isCompatibleType - 测试类型
 *  notNullValue,nullValue - 测试null
 *  sameInstance - 测试是否是同一实例
 *  hasEntry,hasKey,hasValue - 测试一个Map包含entry,key或者value
 *  hasItem,hasItems - 测试一个集合包含对应元素
 *  hasItemInArray - 测试一个数组包含某个元素
 *  closeTo - 测试浮点值接近于给定值
 *  greaterThan, greaterThanOrEqualTo, lessThan, lessThanOrEqualTo
 *  equalToIgnoringCase - 测试字符串相等且忽略大小写
 *  equalToIgnoringWhiteSpace - 测试字符串相等且忽略空白符
 *  containsString, endsWith, startsWith - 匹配字符串

详细请看Hamcrest API: [http://hamcrest.org/JavaHamcrest/javadoc/1.3/org/hamcrest/Matchers.html][http_hamcrest.org_JavaHamcrest_javadoc_1.3_org_hamcrest_Matchers.html]

### 使用Hamcrest内置的匹配器 ###

#### 集合匹配器测试集合 ####

**测试目标**

假设存在下列代码:

List<Integer> list = Arrays.asList(5, 2, 4);

通过使用Hamcrest匹配器对这个list进行下列验证:

*  大小为3
 *  包含2, 4, 5三个元素,忽略顺序
 *  每个元素都大于1

**测试代码**

@Test
    public void hasSizeOf3() {
        List<Integer> list = Arrays.asList(5, 2, 4);
    
        assertThat(list, hasSize(3));
    }

@Test
    public void containsNumbersInAnyOrder() {
        List<Integer> list = Arrays.asList(5, 2, 4);
    
        assertThat(list, containsInAnyOrder(2, 4, 5));
    }

@Test
    public void everyItemGreaterThan1() {
        List<Integer> list = Arrays.asList(5, 2, 4);
    
        assertThat(list, everyItem(greaterThan(1)));
    }

#### 集合匹配器验证数组 ####

**测试目标**

假设存在下列代码:

Integer[] ints = new Integer[] {7, 5, 12, 16};

通过使用Hamcrest匹配器对这个ints数组进行下列验证:

*  长度为4
 *  以特定的顺序含有7, 5, 12, 16元素

**测试代码**

@Test
    public void arrayHasSizeOf4() {
        Integer[] ints = new Integer[] { 7, 5, 12, 16 };
    
        assertThat(ints, arrayWithSize(4));
    }

@Test
    public void arrayContainsNumbersInGivenOrder() {
        Integer[] ints = new Integer[] { 7, 5, 12, 16 };
    
        assertThat(ints, arrayContaining(7, 5, 12, 16));
    }

#### Hamcrest beans匹配器 ####

**测试目标**

假设存在下面的类:

public class Todo {
        private final long id;
        private String summary;
        private String description;
        private int year;
    
        public Todo(long id, String summary, String description) {
            this.id = id;
            this.summary = summary;
            this.description = description;
        }
        //getter 和 setter
    }

通过使用Hamcrest匹配器进行下列验证:

*  Todo类含有名叫 "summary"的属性
 *  如果Todo类被创建时给summary属性传入"Learn Hamcrest", 则summary属性会用这个值进行初始化
 *  两个对象用相同的值创建,会有相同的属性值

**测试代码**

@Test
        public void objectHasSummaryProperty () {
            Todo todo = new Todo(1, "Learn Hamcrest", "Important");
            assertThat(todo, hasProperty("summary"));
        }

@Test
        public void objectHasCorrectSummaryValue () {
            Todo todo = new Todo(1, "Learn Hamcrest", "Important");
            assertThat(todo, hasProperty("summary", equalTo("Learn Hamcrest")));
        }

@Test
        public void objectHasSameProperties () {
            Todo todo1 = new Todo(1, "Learn Hamcrest", "Important");
            Todo todo2 = new Todo(1, "Learn Hamcrest", "Important");
            assertThat(todo1, samePropertyValuesAs(todo2));
        }

#### 字符串匹配器 ####

实现下列对字符串的检查:

*  ""是一个空字符串
 *  一个给定的字符串不是空或者null

@Test
        public void isStringEmpty() {
            String stringToTest = "";
            assertThat(stringToTest, isEmptyString());
        }

@Test
        public void isStringEmptyOfNull() {
            String stringToTest = "";
            assertThat(stringToTest, isEmptyOrNullString());
        }

[http_hamcrest.org_JavaHamcrest_javadoc_1.3_org_hamcrest_Matchers.html]: https://link.jianshu.com?t=http%3A%2F%2Fhamcrest.org%2FJavaHamcrest%2Fjavadoc%2F1.3%2Forg%2Fhamcrest%2FMatchers.html