Fixed NPE on MovieDetailFragmentTest mockk dependency

[cweggler]

Hey @mitchtabian - I ran across a NullPointerException running the MovieDetailFragmentTest when the MoviesRemoteDataSource is mocked via mockk (see stack trace below). Debugging I realized what fixes it is if you mock the interface- MoviesDataSource instead of its implementation. It gets around mockk not knowing how the linkedMap is initialized. Hope this helps other learners!

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object java.util.LinkedHashMap.get(java.lang.Object)' on a null object reference
at com.codingwithmitch.espressouitestexamples.data.source.MoviesRemoteDataSource.getMovie(MoviesRemoteDataSource.kt:21)
at com.codingwithmitch.espressouitestexamples.ui.movie.MovieDetailFragmentTest$test_recreateActivity$1.invoke(MovieDetailFragmentTest.kt:44)
at com.codingwithmitch.espressouitestexamples.ui.movie.MovieDetailFragmentTest$test_recreateActivity$1.invoke(MovieDetailFragmentTest.kt:22)
at io.mockk.impl.eval.RecordedBlockEvaluator$record$block$1.invoke(RecordedBlockEvaluator.kt:24)
at io.mockk.impl.eval.RecordedBlockEvaluator$enhanceWithNPERethrow$1.invoke(RecordedBlockEvaluator.kt:74)
at io.mockk.impl.recording.JvmAutoHinter.autoHint(JvmAutoHinter.kt:23)
at io.mockk.impl.eval.RecordedBlockEvaluator.record(RecordedBlockEvaluator.kt:36)
at io.mockk.impl.eval.EveryBlockEvaluator.every(EveryBlockEvaluator.kt:30)
at io.mockk.MockKDsl.internalEvery(API.kt:92)
at io.mockk.MockKKt.every(MockK.kt:104)
at com.codingwithmitch.espressouitestexamples.ui.movie.MovieDetailFragmentTest.test_recreateActivity(MovieDetailFragmentTest.kt:43)
at java.lang.reflect.Method.invoke(Native Method)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
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.runners.Suite.runChild(Suite.java:128)
at org.junit.runners.Suite.runChild(Suite.java:27)
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$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at org.junit.runner.JUnitCore.run(JUnitCore.java:115)
at androidx.test.internal.runner.TestExecutor.execute(TestExecutor.java:56)
at androidx.test.runner.AndroidJUnitRunner.onStart(AndroidJUnitRunner.java:388)
at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:2074)