Question

我正在使用Android数据绑定来侦听实时数据更改，并且我想观察viewmodel级别的更改（而不是观察片段，然后将回调发送到viewmodel） observerForever很有趣，因为它对我有用。但是，当我运行测试时，出现以下错误：

java.lang.NullPointerException
at androidx.arch.core.executor.DefaultTaskExecutor.isMainThread(DefaultTaskExecutor.java:77)
at androidx.arch.core.executor.ArchTaskExecutor.isMainThread(ArchTaskExecutor.java:116)
at androidx.lifecycle.LiveData.assertMainThread(LiveData.java:461)
at androidx.lifecycle.LiveData.observeForever(LiveData.java:222)
at com.bcgdv.ber.maha.login.ui.LoginViewModel.<init>(LoginViewModel.kt:43)
at com.bcgdv.ber.maha.login.ui.LoginViewModelTest.<init>(LoginViewModelTest.kt:26)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at org.junit.platform.commons.util.ReflectionUtils.newInstance(ReflectionUtils.java:443)
at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:60)

我的代码在viewmodel类中如下：

val observerEmail: Observer<String> = Observer {
    setEmailError(it)
    checkLoginButton()
}
var email = MutableLiveData<String>()
init {
    email.observeForever(observerEmail)
}

还要注意的是，我正在使用Junit5。

@ExtendWith(InstantTaskExecutorExtension::class)
class LoginViewModelTest {
    val emailAddress = "xyz@xyz.com"
    val password = "password"
    val user: User = User("1", "xyz@xyz.com", "password")
val loginUsecase: LoginUseCase = mock {
    on { loginUser(emailAddress, password) } doReturn (Single.just(user))
}

private val loginViewModel: LoginViewModel = LoginViewModel(
    loginUsecase,
    LoginCredentialsValidator(),
    Schedulers.trampoline(),
    Schedulers.trampoline()
)

@Test
fun should_return_user_as_null_initially() {
    whenever(loginUsecase.getUser()).thenReturn(null)
    loginViewModel.init()
    assertEquals(
        expected = null,
        actual = loginViewModel.obsEmail.get()
    )
}}

这是InstantTaskExecutorExtension。

class InstantTaskExecutorExtension : BeforeEachCallback, AfterEachCallback {

override fun beforeEach(context: ExtensionContext?) {
    ArchTaskExecutor.getInstance()
            .setDelegate(object : TaskExecutor() {
                override fun executeOnDiskIO(runnable: Runnable) = runnable.run()

                override fun postToMainThread(runnable: Runnable) = runnable.run()

                override fun isMainThread(): Boolean = true
            })
}

override fun afterEach(context: ExtensionContext?) {
    ArchTaskExecutor.getInstance().setDelegate(null)
}

}

Answer 1

通常，建议仅将LiveData用于View模型<-> View通讯，但是我认为问题是：

private val loginViewModel: LoginViewModel = LoginViewModel(
    ...
)

由于这是一个成员变量，因此它将在测试之前执行，并且由于调用构造函数而已隐式执行init()。无需显式调用init()。我将删除loginViewModel成员变量，并通过构造函数在测试函数中实例化它：

@Test
fun should_return_user_as_null_initially() {
    ...
    LoginViewModel(
       ...
    )
    ...
}

对LiveData Observer进行单元测试会导致Junit5出现NullPointer异常

1 个答案: