官方地址：http://joel-costigliola.github.io/assertj/ 开源地址：https://github.com/joel-costigliola/assertj-core
从官网上我们可以看到AssertJ支持的库有这些，具体用法上官方查询：
Core：AssertJ core is a Java library that provides a fluent interface for writing assertions.
Assertions generator：Use the Assertion Generator to create assertions specific to your own classes.
Guava：AssertJ assertions for Guava provides assertions for Guava types like Multimap, Table, Optional, Range or ByteSource.
Joda-Time：AssertJ assertions for Joda-Time provides assertions for Joda-Time types like DateTime and LocalDateTime.
DB：AssertJ-DB provides assertions to test data in a database.
Neo4j：Provides assertions for Neo4j 2 or higher.
Swing：AssertJ Swing is a Java library that provides a fluent interface for functional Swing UI testing.
maven引入依赖如下：
<dependency> <groupId>org.assertj</groupId> <artifactId>assertj-core</artifactId> <!-- use 3.0.0 for Java 8 projects --> <!-- 2.0.0 required Java 7 --> <!-- 1.7.1 for Java 6 --> <version>1.7.1</version> <scope>test</scope> </dependency>此外对应的开发库引入如下：
<dependency> <groupId>org.assertj</groupId> <artifactId>assertj-joda-time</artifactId> <version>1.1.0</version> <scope>test</scope> </dependency> <dependency> <groupId>org.assertj</groupId> <artifactId>assertj-guava</artifactId> <version>2.0.0</version> <scope>test</scope> <exclusions> <exclusion> <groupId>org.assertj</groupId> <artifactId>assertj-core</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.assertj</groupId> <artifactId>assertj-neo4j</artifactId> <version>1.0.0</version> <scope>test</scope> </dependency> <dependency> <groupId>org.assertj</groupId> <artifactId>assertj-db</artifactId> <version>1.0.1</version> <scope>test</scope> </dependency>官方上的用法介绍：
// 为所有assertThat和工具方法提供唯一访问入口（例如entry） import static org.assertj.core.api.Assertions.*; // 下面的示例中，fellowshipOfTheRing是一个TolkienCharacter列表 // 简单断言 assertThat(frodo.getName()).isEqualTo("Frodo"); assertThat(frodo).isNotEqualTo(sauron) .isIn(fellowshipOfTheRing); // String断言 assertThat(frodo.getName()).startsWith("Fro") .endsWith("do") .isEqualToIgnoringCase("frodo"); // 集合断言 assertThat(fellowshipOfTheRing).hasSize(9) .contains(frodo, sam) .doesNotContain(sauron); // 使用extracting特性检查fellowshipOfTheRing中的名字:) assertThat(fellowshipOfTheRing).extracting("name").contains("Boromir", "Gandalf", "Frodo", "Legolas") .doesNotContain("Sauron", "Elrond"); // Java 8方式的extracting assertThat(fellowshipOfTheRing).extracting(character -> character.getRace().getName()) .contains("Hobbit", "Elf") .doesNotContain("Orc"); // 断言之前过滤集合 assertThat(fellowshipOfTheRing).filteredOn("race", HOBBIT) .containsOnly(sam, frodo, pippin, merry); // 使用Java 8 lambda predicate过滤集合 assertThat(fellowshipOfTheRing).filteredOn(character -> character.getName().contains("o")) .containsOnly(aragorn, frodo, legolas, boromir); // 将extraction和过滤结合（是的，我们可以做到） assertThat(fellowshipOfTheRing).filteredOn(character -> character.getName().contains("o")) .containsOnly(aragorn, frodo, legolas, boromir) .extracting(character -> character.getRace().getName()) .contains("Hobbit", "Elf", "Man");个人常用到的一些方法： String 校验
@Test public void testString() { String str = null; // 断言null或为空字符串 assertThat(str).isNullOrEmpty(); // 断言空字符串 assertThat("").isEmpty(); // 断言字符串相等 断言忽略大小写判断字符串相等 assertThat("Frodo").isEqualTo("Frodo").isEqualToIgnoringCase("frodo"); // 断言开始字符串 结束字符穿 字符串长度 assertThat("Frodo").startsWith("Fro").endsWith("do").hasSize(5); // 断言包含字符串 不包含字符串 assertThat("Frodo").contains("rod").doesNotContain("fro"); // 断言字符串只出现过一次 assertThat("Frodo").containsOnlyOnce("do"); // 判断正则匹配 assertThat("Frodo").matches("..o.o").doesNotMatch(".*d"); }数字校验
@Test public void testNumber() { Integer num = null; // 断言空 assertThat(num).isNull(); // 断言相等 assertThat(42).isEqualTo(42); // 断言大于 大于等于 assertThat(42).isGreaterThan(38).isGreaterThanOrEqualTo(38); // 断言小于 小于等于 assertThat(42).isLessThan(58).isLessThanOrEqualTo(58); // 断言0 assertThat(0).isZero(); // 断言正数 非负数 assertThat(1).isPositive().isNotNegative(); // 断言负数 非正数 assertThat(-1).isNegative().isNotPositive(); }时间断言
@Test public void testDate() { // 断言与指定日期相同 不相同 在指定日期之后 在指定日期之钱 assertThat(Dates.parse("2014-02-01")).isEqualTo("2014-02-01").isNotEqualTo("2014-01-01") .isAfter("2014-01-01").isBefore(parse("2014-03-01")); // 断言 2014 在指定年份之前 在指定年份之后 assertThat(DateTime.now().toDate()).isBeforeYear(2020).isAfterYear(2013); // 断言时间再指定范围内 不在指定范围内 assertThat(parse("2014-02-01")).isBetween("2014-01-01", "2014-03-01").isNotBetween( parse("2014-02-02"), parse("2014-02-28"));List断言
@Test public void testList() { // 断言 列表是空的 assertThat(newArrayList()).isEmpty(); // 断言 列表的开始 结束元素 assertThat(newArrayList(1, 2, 3)).startsWith(1).endsWith(3); // 断言 列表包含元素 并且是排序的 assertThat(newArrayList(1, 2, 3)).contains(1, atIndex(0)).contains(2, atIndex(1)).contains(3) .isSorted(); // 断言 被包含与给定列表 assertThat(newArrayList(3, 1, 2)).isSubsetOf(newArrayList(1, 2, 3, 4)); // 断言 存在唯一元素 assertThat(Lists.newArrayList("a", "b", "c")).containsOnlyOnce("a"); }Map断言
@Test public void testMap() { Map<String, Object> foo = Maps.newHashMap(); foo.put("A", 1); foo.put("B", 2); foo.put("C", 3); // 断言 map 不为空 size assertThat(foo).isNotEmpty().hasSize(3); // 断言 map 包含元素 assertThat(foo).contains(entry("A", 1), entry("B", 2)); // 断言 map 包含key assertThat(foo).containsKeys("A", "B", "C"); // 断言 map 包含value assertThat(foo).containsValue(3); }添加错误提示信息： as
assertThat("abc").as("校验abc").isEqualTo("abcd"); 错误提示： org.junit.ComparisonFailure: [校验abc] expected:<"abc[d]"> but was:<"abc[]">链式校验
// isEqualTo 相等， contains包含 assertThat("abc").as("校验abc").isEqualTo("abc").contains("d"); 错误提示： FAILED: testAssertJ java.lang.AssertionError: [校验abc] Expecting: <"abc"> to contain: <"d">大小校验
List list = new ArrayList(); assertThat(list).hasSize(1); FAILED: testAssertJ java.lang.AssertionError: Expected size:<1> but was:<0> in: <[]>null判断
Object object = null; assertThat(object).isNotNull(); assertThat(object).isNull();同时，AssertJ还支持自定义断言，就是根据自己的需求，自定义断言类型。
