Assertions

JUnit提供了许多重载的断言方法，这些方法均可以通过"import static org.junit.Assert.*"导入。方法的参数顺序一般都是([失败时打印的字符串消息]，期望值，实际值)。

特别要提到的一种断言是assertThat，它的参数是([失败时打印的字符串消息]，实际值，Matcher对象)，参数顺序和其他的断言方法正好相反。同时由于生成Matcher对象需要用到”org.hamcrest.CoreMatchers.*"里面的方法，所以使用assertThat的时候需要额外导入hamcrest-core.jar和hamcrest-library.jar （下载地址：http://search.maven.org/#search|ga|1|g%3Aorg.hamcrest）。关于AssertThat的详细介绍参见 ”Matchers and assertthat"。

Hamcrest是什么呢？它的官网是这样说的：amcrest is a library of matchers, which can be combined in to create flexible expressions of intent in tests。按我的理解就是Hamcrest是一个Library，它提供了一套匹配符Matcher，这些匹配符可读性高而且灵活，所以JUnit4引入了Hamcrest框架。

Hamcrest官网：http://hamcrest.org/。

Hamcrest主页：http://code.google.com/p/hamcrest/wiki/Tutorial

Hamcrest整个包在GitHub的下载地址：https://github.com/hamcrest/JavaHamcrest

官网的断言示例如下：

import static org.junit.Assert.*;
import static org.hamcrest.CoreMatchers.*;import java.util.Arrays;
import org.hamcrest.core.CombinableMatcher;
import org.junit.Test;public class AssertTests {@Testpublic void testAssertArrayEquals(){byte[] expected="trial".getBytes();byte[] actual="trial".getBytes();assertArrayEquals("failure-byte arrays not same",expected, actual);}@Testpublic void testAssertEquals(){assertEquals("failure-strings are not equal","test","test");}@Testpublic void testAssertFalse(){assertFalse("failure-should be false",false);}@Testpublic void testAssertNotNull(){assertNotNull("should not be null",new Object());}@Testpublic void testAssertNotSame(){assertNotSame("should not be same object",new Object(),new String("hello"));}@Testpublic void testAssertNull(){assertNull("should be null",null);}@Testpublic void testAssertSame(){Integer aNumber=Integer.valueOf(78);assertSame("should be the same",aNumber,aNumber);}// JUnit Matchers assertThat@Testpublic void testAssertThatBothContainsString() {org.junit.Assert.assertThat("albumen", both(containsString("a")).and(containsString("b")));}@Testpublic void testAssertThathasItemsContainsString() {org.junit.Assert.assertThat(Arrays.asList("one", "two", "three"), hasItems("one", "three"));}@Testpublic void testAssertThatEveryItemContainsString() {org.junit.Assert.assertThat(Arrays.asList(new String[] { "fun", "ban", "net" }), everyItem(containsString("n")));}// Core Hamcrest Matchers with assertThat@Testpublic void testAssertThatHamcrestCoreMatchers() {assertThat("good", allOf(equalTo("good"), startsWith("good")));assertThat("good", not(allOf(equalTo("bad"), equalTo("good"))));assertThat("good", anyOf(equalTo("bad"), equalTo("good")));assertThat(7, not(CombinableMatcher. either(equalTo(3)).or(equalTo(4))));assertThat(new Object(), not(sameInstance(new Object())));}@Testpublic void testAssertTrue() {assertTrue("failure - should be true", true);}	
}

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