参照 Android Studio 3.6.3/4.0/4.1/4.2配置Robolectric-3.8/4.3.1/4.5.1/4.6.1 Powermock-1.6.6单元测试环境 进行单元测试，不过，由于工程的限制(不能依赖 AndroidX)，我们只能在 Robolectric 3.8 。
Android Studio 4.1.3，JDK使用 Java 1.8
在执行如下测试用例的时候，发现当被测试代码使用 Executors 在子线程执行的时候，如果使用 Powermock 的 WhenNew 对被测试对象进行仿真的时候，无法正确的被 Mock。
被测试代码如下：
import android.support.annotation.NonNull;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class CustomExecutor {
private final static String TAG = "CustomExecutor";
private static volatile CustomExecutor instance;
private CustomMocker custom;
private final ExecutorService executor = Executors.newSingleThreadExecutor();
private CustomExecutor() {
executor.submit(new Runnable() {
@Override
public void run() {
custom = new CustomMocker();
}
});
}
@NonNull
public static CustomExecutor getInstance() {
if (null == instance) {
synchronized (CustomExecutor.class) {
if (null == instance) {
instance = new CustomExecutor();
}
}
}
return instance;
}
public String getMessage() throws Exception {
final Future<String> future = executor.submit(new Callable<String>() {
@Override
public String call() {
return custom.getMessage();
}
});
return future.get();
}
}
public class CustomMocker {
public String getMessage() {
return "I am not mocked";
}
}
单元测试代码如下：
import org.junit.Assert;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PowerMockIgnore;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.rule.PowerMockRule;
import org.robolectric.RobolectricTestRunner;
import org.robolectric.annotation.Config;
@RunWith(RobolectricTestRunner.class)
@PowerMockIgnore({"org.mockito.*", "org.robolectric.*", "android.*"})
@PrepareForTest({CustomMocker.class, CustomExecutor.class})
@Config(manifest = Config.NONE, constants = BuildConfig.class, sdk = 26)
public class CustomExecutorTest {
@Rule
public final PowerMockRule rule = new PowerMockRule();
@Before
public void setup() throws Exception {
final CustomMocker clz = PowerMockito.mock(CustomMocker.class);
PowerMockito.when(clz.getMessage()).thenReturn("I am mocked!");
PowerMockito.whenNew(CustomMocker.class).withAnyArguments().thenReturn(clz);
}
@Test
public void testCustomExecutors() {
final CustomExecutor executor = CustomExecutor.getInstance();
Assert.assertNotNull(executor);
Assert.assertEquals(expStr, executor.getMessage());
}
}
上述的测试代码在执行的时候，完全不会生效。
网上查询了一下，根据 Unable to get mocked instance of Executor in separate class 的介绍，我们需要在测试用例里面的`@PrepareForTest`里面增加 `Executors.class`，于是修改测试用例为如下：
import org.junit.Assert;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PowerMockIgnore;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
import org.powermock.modules.junit4.PowerMockRunnerDelegate;
import org.powermock.modules.junit4.rule.PowerMockRule;
import org.robolectric.RobolectricTestRunner;
import org.robolectric.annotation.Config;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
@RunWith(PowerMockRunner.class)
@PowerMockRunnerDelegate(RobolectricTestRunner.class)
@PowerMockIgnore({"jdk.internal.reflect.*", "org.apache.commons.*", "org.mockito.*", "org.robolectric.*", "android.*"})
@PrepareForTest({ExecutorService.class, Executors.class, CustomMocker.class, CustomExecutor.class})
@Config(sdk = 26)
public class CustomExecutorTest {
private final static String expStr = "I am mocked!";
@Rule
public final PowerMockRule rule = new PowerMockRule();
@Before
public void setup() throws Exception {
PowerMockito.mockStatic(Executors.class);
PowerMockito.mockStatic(ExecutorService.class);
PowerMockito.when(Executors.newSingleThreadExecutor()).thenCallRealMethod();
PowerMockito.mockStatic(CustomExecutor.class);
final CustomMocker clz = PowerMockito.mock(CustomMocker.class);
PowerMockito.when(clz.getMessage()).thenReturn(expStr);
PowerMockito.whenNew(CustomMocker.class).withAnyArguments().thenReturn(clz);
PowerMockito.mockStatic(CustomExecutor.class);
PowerMockito.when(CustomExecutor.getInstance()).thenCallRealMethod();
}
@Test
public void testExecutorsMock() throws Exception {
final CustomExecutor executor = CustomExecutor.getInstance();
Assert.assertNotNull(executor);
Assert.assertEquals(expStr, executor.getMessage());
}
}
结果出现一个诡异的现象，如果在创建对象的地方设置断点进行调试跟踪，就是正确的，去掉断点，就会失败。
这个问题卡住很久，结果突然想起以前写的一个差不多功能的被测试类，是能正常工作的，于是进行了代码对比，结果发现一个奇怪的现象，只要内部定义一个类来中继一下，就可以完美解决问题。于是修改被测试类，代码如下：
import android.support.annotation.NonNull;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class CustomExecutor {
private static volatile CustomExecutor instance;
@NonNull
private final ExecutorService executor = Executors.newSingleThreadExecutor();
private Delegate delegate;
private CustomExecutor() {
executor.submit(new Runnable() {
@Override
public void run() {
delegate = new Delegate();
}
});
}
@NonNull
public static CustomExecutor getInstance() {
if (null == instance) {
synchronized (CustomExecutor.class) {
if (null == instance) {
instance = new CustomExecutor();
}
}
}
return instance;
}
public String getMessage() throws Exception {
final Future<String> future = executor.submit(new Callable<String>() {
@Override
public String call() {
return delegate.getMessage();
}
});
return future.get();
}
private static class Delegate {
private final CustomMocker mocker;
public Delegate() {
mocker = new CustomMocker();
}
public String getMessage() {
return mocker.getMessage();
}
}
}
也就是内部定义来一个代理子类，初始化的时候，通过内部子类进行初始化。
这个现象比较奇怪，目前能解决问题，具体原因还是不详。