Mocking Android Snackbar for Mockk Unit Testing

Question

I want to to mock the Snackbar class, but the initialization code below keeps throwing errors.

    @MockK
    lateinit var snackbar: Snackbar

It looks like the mock initalizer has to access BaseTransientBottomBar's static method, which calls Android.os.Looper.getMainLooper(). Here is the error log:

java.lang.ExceptionInInitializerError
    at sun.reflect.GeneratedSerializationConstructorAccessor4.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at org.objenesis.instantiator.sun.SunReflectionFactoryInstantiator.newInstance(SunReflectionFactoryInstantiator.java:48)
    at io.mockk.proxy.jvm.ObjenesisInstantiator.instanceViaObjenesis(ObjenesisInstantiator.kt:75)
    at io.mockk.proxy.jvm.ObjenesisInstantiator.instance(ObjenesisInstantiator.kt:42)
    at io.mockk.proxy.jvm.ProxyMaker.instantiate(ProxyMaker.kt:75)
    at io.mockk.proxy.jvm.ProxyMaker.proxy(ProxyMaker.kt:42)
    at io.mockk.impl.instantiation.JvmMockFactory.newProxy(JvmMockFactory.kt:34)
    at io.mockk.impl.instantiation.AbstractMockFactory.newProxy$default(AbstractMockFactory.kt:29)
    at io.mockk.impl.instantiation.AbstractMockFactory.mockk(AbstractMockFactory.kt:59)
    at io.mockk.impl.annotations.JvmMockInitializer.assignMockK(JvmMockInitializer.kt:145)
    at io.mockk.impl.annotations.JvmMockInitializer.initMock(JvmMockInitializer.kt:39)
    at io.mockk.impl.annotations.JvmMockInitializer.initAnnotatedMocks(JvmMockInitializer.kt:22)
    at com.example.MyTest.<init>(MyTest.kt:155)
    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.runners.BlockJUnit4ClassRunner.createTest(BlockJUnit4ClassRunner.java:217)
    at org.junit.runners.BlockJUnit4ClassRunner$1.runReflectiveCall(BlockJUnit4ClassRunner.java:266)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.BlockJUnit4ClassRunner.methodBlock(BlockJUnit4ClassRunner.java:263)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)
Caused by: java.lang.RuntimeException: Method getMainLooper in android.os.Looper not mocked. See http://g.co/androidstudio/not-mocked for details.
    at android.os.Looper.getMainLooper(Looper.java)
    at com.google.android.material.snackbar.BaseTransientBottomBar.<clinit>(BaseTransientBottomBar.java:185)
    ... 35 more

Does anyone know how to solve this problem? Thank you in advance.

Answer 1

You have only created an object of type Snackbar but did not assigned any value to it.

It should be like -> val snackbar: Snackbar = Snackbar();