java - @BeforeClass 和 @AfterClass 在每次测试之前和之后调用

Question

我有一个非常简单的测试类，用于在 Android 上运行 espresso 测试，如下所示:

import android.util.Log;

import org.junit.After;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.ClassRule;
import org.junit.Test;
import org.junit.rules.ExternalResource;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

import java.io.IOException;

@RunWith(JUnit4.class)
public class Wtf {

    private static class TestResources extends ExternalResource {
        protected void before() {
            println("before() TestResources");
        }
        protected void after() {
            println("after() TestResources");
        }
    }

    @ClassRule
    public static final TestResources res = new TestResources();

    @BeforeClass
    public static void setUpClass() {
        println("@BeforeClass setUpClass()");
    }

    @AfterClass
    public static void tearDownClass() throws IOException {
        println("@AfterClass tearDownClass()");
    }

    private static void println(String string) {
        Log.d("wow", Wtf.class.getSimpleName() + ": " + string);
    }

    @Before
    public void setUp() {
        this.println("@Before setUp()");
    }

    @After
    public void tearDown() throws IOException {
        this.println("@After tearDown()");
    }

    @Test
    public void test_1() {
        this.println("@Test test1()");
    }

    @Test
    public void test_2() {
        this.println("@Test test2()");
    }
}

输出如下所示:

D/wow: Wtf: before() TestResources
D/wow: Wtf: @BeforeClass setUpClass()
D/wow: Wtf: @Before setUp()
D/wow: Wtf: @Test test1()
D/wow: Wtf: @After tearDown()
D/wow: Wtf: @AfterClass tearDownClass()
D/wow: Wtf: after() TestResources
D/wow: Wtf: before() TestResources
D/wow: Wtf: @BeforeClass setUpClass()
D/wow: Wtf: @Before setUp()
D/wow: Wtf: @Test test2()
D/wow: Wtf: @After tearDown()
D/wow: Wtf: @AfterClass tearDownClass()
D/wow: Wtf: after() TestResources

但我希望在整个类(class)运行后调用一些东西。难道我做错了什么？为什么每次测试之前和之后都会调用 @BeforeClass 和 @AfterClass 方法？

Answer 1

事实证明这是由于 Android Test Orchestrator :

Each test runs in its own Instrumentation instance. Therefore, if your tests share app state, most of that shared state is removed from your device's CPU or memory after each test.

我不知道解决方法，但至少现在我知道为什么会发生。