JUnit4注解基本介绍
JUnit4 中@AfterClass @BeforeClass @after @before的区别对比
junit之测试顺序
1、JUnit4基本注解
@Before
When writing tests, it is common to find that several tests need similar objects created before they can run. Annotating a public void method with @Before causes that method to be run before the Test method. The @Before methods of superclasses will be run before those of the current class. No other ordering is defined.
当编写测试方法时，经常会发现一些方法在执行前需要创建相同的对象。使用@Before注解一个public void 方法会使该方法在每个@Test注解方法被执行前执行（那么就可以在该方法中创建相同的对象）。
父类的@Before注解方法会在子类的@Before注解方法执行前执行。
@After
If you allocate external resources in a Before method you need to release them after the test runs.Annotating a public void method with @After causes that method to be run after the Test method. All @After methods are guaranteed to run even if a Before or Test method throws an exception. The @After methods declared in superclasses will be run after those of the current class.
使用@After注解一个public void方法会使该方法在每个@Test注解方法执行后被执行。
如果在@Before注解方法中分配了额外的资源，那么在测试执行完后，需要释放分配的资源，这个释放资源的操作可以在After中完成。
即使在@Before注解方法、@Test注解方法中抛出了异常，所有的@After注解方法依然会被执行。
父类中的@After注解方法会在子类@After注解方法执行后被执行。
@Test
The Test annotation tells JUnit that the public void method to which it is attached can be run as a test case. To run the method, JUnit first constructs a fresh instance of the class then invokes the annotated method. Any exceptions thrown by the test will be reported by JUnit as a failure. If no exceptions are thrown, the test is assumed to have succeeded.
The Test annotation supports two optional parameters.
The first, expected,declares that a test method should throw an exception. If it doesn't throw an exception or if it throws a different exception than the one declared, the test fails.
The second optional parameter, timeout, causes a test to fail if it takes longer than a specified amount of clock time (measured in milliseconds).
@Test注解的public void方法将会被当做测试用例，JUnit每次都会创建一个新的测试实例，然后调用@Test注解方法，任何异常的抛出都会认为测试失败。当以一个类为测试单元时，所有测试用例（测试方法）共属同一个测试实例（具有同一个环境）；当以一个方法为测试单元时，JUnit每次都会创建一个新的测试实例。
@Test注解提供2个参数：
1，“expected”，定义测试方法应该抛出的异常，如果测试方法没有抛出异常或者抛出了一个不同的异常，测试失败；
2，“timeout”，如果测试运行时间长于该定义时间，测试失败（单位为毫秒）。
@BeforeClass
Sometimes several tests need to share computationally expensive setup (like logging into a database). While this can compromise the independence of tests, sometimes it is a necessary optimization.Annotating a public static void no-arg method with @BeforeClass causes it to be run once before any of the test methods in the class. The @BeforeClass methods of superclasses will be run before those the current class.
有些时候，一些测试需要共享代价高昂的步骤（如数据库登录），这会破坏测试独立性，通常是需要优化的。
使用@BeforeClass注解一个public static void 方法，并且该方法不带任何参数，会使该方法在所有测试方法被执行前执行一次，并且只执行一次。
父类的@BeforeClass注解方法会在子类的@BeforeClass注解方法执行前执行。
@AfterClass
If you allocate expensive external resources in a Before Class method you need to release them after all the tests in the class have run. Annotating a public static void method with @AfterClass causes that method to be run after all the tests in the class have been run. All @AfterClass methods are guaranteed to run even if a Before Class method throws an exception.The @AfterClass methods declared in superclasses will be run after those of thecurrent class.
如果在@BeforeClass注解方法中分配了代价高昂的额外的资源，那么在测试类中的所有测试方法执行完后，需要释放分配的资源。
使用@AfterClass注解一个public static void方法会使该方法在测试类中的所有测试方法执行完后被执行。
即使在@BeforeClass注解方法中抛出了异常，所有的@AfterClass注解方法依然会被执行。
父类中的@AfterClass注解方法会在子类@AfterClass注解方法执行后被执行。
@Ignore
Sometimes you want to temporarily disable a test or a group of tests. Methods annotated with Test that are also annotated with @Ignore will not be executed as tests. Also, you can annotate a class containing test methods with @Ignore and none of the containing tests will be executed. Native JUnit 4 test runners should report the number of ignored tests along with the number of tests that ran and the number of tests that failed.
对包含测试类的类或@Test注解方法使用@Ignore注解将使被注解的类或方法不会被当做测试执行；JUnit执行结果中会报告被忽略的测试数。
2、Junit测试顺序：@FixMethodOrder
Junit 4.11里增加了指定测试方法执行顺序的特性，测试类的执行顺序可通过对测试类添加注解 @FixMethodOrder(value)来指定,其中value 为执行顺序 ，下面是value值下对应的测试顺序行为：
-
** MethodSorters.DEFAULT **（默认）
默认顺序由方法名hashcode值来决定，如果hash值大小一致，则按名字的字典顺序确定。
由于hashcode的生成和操作系统相关(以native修饰），所以对于不同操作系统，可能会出现不一样的执行顺序，在某一操作系统上，多次执行的顺序不变 。 -
** MethodSorters.NAME_ASCENDING （推荐） **
按方法名称的进行排序，由于是按字符的字典顺序，所以以这种方式指定执行顺序会始终保持一致；
不过这种方式需要对测试方法有一定的命名规则，如 测试方法均以testNNN开头（NNN表示测试方法序列号 001-999） 。 -
** MethodSorters.JVM **
按JVM返回的方法名的顺序执行，此种方式下测试方法的执行顺序是不可预测的，即每次运行的顺序可能
都不一样(JDK7里尤其如此)。
3、栗子
import org.junit.*;
import org.junit.runners.MethodSorters;
@FixMethodOrder(value = MethodSorters.DEFAULT) // <<--- I will change here for testing ...
public class MathTest {
private static int flag = 0;
@Test(timeout = 1000)
public void testA(){
System.out.println("here is testA");
System.out.println("flag = " + flag);
flag = 1;
System.out.println("flag = " + flag);
}
@Test
public void testB(){
System.out.println("here is testB");
System.out.println("flag = " + flag);
flag = 2;
System.out.println("flag = " + flag);
}
@Test
public void testC(){
System.out.println("here is testC");
System.out.println("flag = " + flag);
flag = 3;
System.out.println("flag = " + flag);
}
@Before
public void beforeEveryTest(){
System.out.println("\n=== beforeEveryTest ===\n");
}
@After
public void afterEveryTest(){
System.out.println("\n=== afterEveryTest ===\n");
}
// must be static
@BeforeClass
public static void beforeClassTest(){
System.out.println("\n===beforeClassTest===\n");
}
// must be static
@AfterClass
public static void afterClassTest(){
System.out.println("\n===afterClassTest===\n");
}
}
默认顺序
===beforeClassTest===
=== beforeEveryTest ===
here is testA
flag = 0
flag = 1
=== afterEveryTest ===
=== beforeEveryTest ===
here is testB
flag = 1
flag = 2
=== afterEveryTest ===
=== beforeEveryTest ===
here is testC
flag = 2
flag = 3
=== afterEveryTest ===
===afterClassTest===
字典顺序
同上
JVM顺序
===beforeClassTest===
=== beforeEveryTest ===
here is testB
flag = 0
flag = 2
=== afterEveryTest ===
=== beforeEveryTest ===
here is testA
flag = 2
flag = 1
=== afterEveryTest ===
=== beforeEveryTest ===
here is testC
flag = 1
flag = 3
=== afterEveryTest ===
===afterClassTest===
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