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

Method Summarystatic voidassertArrayEquals(boolean[] expecteds, boolean[] actuals)
          Asserts that two boolean arrays are equal.static voidassertArrayEquals(byte[] expecteds, byte[] actuals)
          Asserts that two byte arrays are equal.static voidassertArrayEquals(char[] expecteds, char[] actuals)
          Asserts that two char arrays are equal.static voidassertArrayEquals(double[] expecteds, double[] actuals, double delta)
          Asserts that two double arrays are equal.static voidassertArrayEquals(float[] expecteds, float[] actuals, float delta)
          Asserts that two float arrays are equal.static voidassertArrayEquals(int[] expecteds, int[] actuals)
          Asserts that two int arrays are equal.static voidassertArrayEquals(long[] expecteds, long[] actuals)
          Asserts that two long arrays are equal.static voidassertArrayEquals(Object[] expecteds,Object[] actuals)
          Asserts that two object arrays are equal.static voidassertArrayEquals(short[] expecteds, short[] actuals)
          Asserts that two short arrays are equal.static voidassertArrayEquals(String message, boolean[] expecteds, boolean[] actuals)
          Asserts that two boolean arrays are equal.static voidassertArrayEquals(String message, byte[] expecteds, byte[] actuals)
          Asserts that two byte arrays are equal.static voidassertArrayEquals(String message, char[] expecteds, char[] actuals)
          Asserts that two char arrays are equal.static voidassertArrayEquals(String message, double[] expecteds, double[] actuals, double delta)
          Asserts that two double arrays are equal.static voidassertArrayEquals(String message, float[] expecteds, float[] actuals, float delta)
          Asserts that two float arrays are equal.static voidassertArrayEquals(String message, int[] expecteds, int[] actuals)
          Asserts that two int arrays are equal.static voidassertArrayEquals(String message, long[] expecteds, long[] actuals)
          Asserts that two long arrays are equal.static voidassertArrayEquals(String message,Object[] expecteds,Object[] actuals)
          Asserts that two object arrays are equal.static voidassertArrayEquals(String message, short[] expecteds, short[] actuals)
          Asserts that two short arrays are equal.static voidassertEquals(double expected, double actual)
          Deprecated. Use assertEquals(double expected, double actual, double delta) insteadstatic voidassertEquals(double expected, double actual, double delta)
          Asserts that two doubles are equal to within a positive delta.static voidassertEquals(float expected, float actual, float delta)
          Asserts that two floats are equal to within a positive delta.static voidassertEquals(long expected, long actual)
          Asserts that two longs are equal.static voidassertEquals(Object[] expecteds,Object[] actuals)
          Deprecated. use assertArrayEqualsstatic voidassertEquals(Object expected,Object actual)
          Asserts that two objects are equal.static voidassertEquals(String message, double expected, double actual)
          Deprecated. Use assertEquals(String message, double expected, double actual, double delta) insteadstatic voidassertEquals(String message, double expected, double actual, double delta)
          Asserts that two doubles are equal to within a positive delta.static voidassertEquals(String message, float expected, float actual, float delta)
          Asserts that two floats are equal to within a positive delta.static voidassertEquals(String message, long expected, long actual)
          Asserts that two longs are equal.static voidassertEquals(String message,Object[] expecteds,Object[] actuals)
          Deprecated. use assertArrayEqualsstatic voidassertEquals(String message,Object expected,Object actual)
          Asserts that two objects are equal.static voidassertFalse(boolean condition)
          Asserts that a condition is false.static voidassertFalse(String message, boolean condition)
          Asserts that a condition is false.static voidassertNotEquals(double unexpected, double actual, double delta)
          Asserts that two doubles are not equal to within a positive delta.static voidassertNotEquals(float unexpected, float actual, float delta)
          Asserts that two floats are not equal to within a positive delta.static voidassertNotEquals(long unexpected, long actual)
          Asserts that two longs are not equals.static voidassertNotEquals(Object unexpected,Object actual)
          Asserts that two objects are not equals.static voidassertNotEquals(String message, double unexpected, double actual, double delta)
          Asserts that two doubles are not equal to within a positive delta.static voidassertNotEquals(String message, float unexpected, float actual, float delta)
          Asserts that two floats are not equal to within a positive delta.static voidassertNotEquals(String message, long unexpected, long actual)
          Asserts that two longs are not equals.static voidassertNotEquals(String message,Object unexpected,Object actual)
          Asserts that two objects are not equals.static voidassertNotNull(Object object)
          Asserts that an object isn't null.static voidassertNotNull(String message,Object object)
          Asserts that an object isn't null.static voidassertNotSame(Object unexpected,Object actual)
          Asserts that two objects do not refer to the same object.static voidassertNotSame(String message,Object unexpected,Object actual)
          Asserts that two objects do not refer to the same object.static voidassertNull(Object object)
          Asserts that an object is null.static voidassertNull(String message,Object object)
          Asserts that an object is null.static voidassertSame(Object expected,Object actual)
          Asserts that two objects refer to the same object.static voidassertSame(String message,Object expected,Object actual)
          Asserts that two objects refer to the same object.static <T> voidassertThat(String reason, T actual, Matcher<? super T> matcher)
          Asserts that actual satisfies the condition specified by matcher.static <T> voidassertThat(T actual,Matcher<? super T> matcher)
          Asserts that actual satisfies the condition specified by matcher.static voidassertTrue(boolean condition)
          Asserts that a condition is true.static voidassertTrue(String message, boolean condition)
          Asserts that a condition is true.static voidfail()
          Fails a test with no message.static voidfail(String message)

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  @Test  public void testAssertThatBothContainsString() {    org.junit.Assert.assertThat("albumen", both(containsString("a")).and(containsString("b")));  }  @Test  public void testAssertThathasItemsContainsString() {    org.junit.Assert.assertThat(Arrays.asList("one", "two", "three"), hasItems("one", "three"));  }  @Test  public void testAssertThatEveryItemContainsString() {    org.junit.Assert.assertThat(Arrays.asList(new String[] { "fun", "ban", "net" }), everyItem(containsString("n")));  }  // Core Hamcrest Matchers with assertThat  @Test  public 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.<Integer> either(equalTo(3)).or(equalTo(4))));    assertThat(new Object(), not(sameInstance(new Object())));  }  @Test  public void testAssertTrue() {    assertTrue("failure - should be true", true);  }}