其实在之前的文章中已经使用过 Hamcrest 匹配器框架,本篇文章将系统的介绍它的使用.
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.
下面的代码就是一个使用Hamcrest的案例.
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)
// ...
使用Hamcrest匹配器也具备更高的类型安全性, 因为它们都使用了泛型.
添加Hamcrest依赖
对于Android Studio,需要在build.gradle中添加:
dependencies {
// Unit testing dependencies
testImplementation 'junit:junit:4.12'
// Set this dependency if you want to use Hamcrest matching
testImplementation 'org.hamcrest:hamcrest-library:1.3'
}
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
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());
}
敲行代码再睡觉
