Add DatabaseMocker to mock NewPipeDatabase

app/src/androidTest/java/org/schabi/newpipe/local/playlist/LocalPlaylistManagerTest.kt

@@ -1,7 +1,5 @@
 package org.schabi.newpipe.local.playlist
 
-import androidx.room.Room
-import androidx.test.core.app.ApplicationProvider
 import org.junit.After
 import org.junit.Before
 import org.junit.Rule
@@ -10,6 +8,7 @@ import org.junit.rules.Timeout
 import org.schabi.newpipe.database.AppDatabase
 import org.schabi.newpipe.database.stream.model.StreamEntity
 import org.schabi.newpipe.extractor.stream.StreamType
+import org.schabi.newpipe.testUtil.TestDatabase
 import org.schabi.newpipe.testUtil.TrampolineSchedulerRule
 import java.util.concurrent.TimeUnit
 
@@ -22,17 +21,11 @@ class LocalPlaylistManagerTest {
     val trampolineScheduler = TrampolineSchedulerRule()
 
     @get:Rule
-    val timeout = Timeout(10, TimeUnit.SECONDS)
+    val timeout = Timeout(1, TimeUnit.SECONDS)
 
     @Before
     fun setup() {
-        database = Room.inMemoryDatabaseBuilder(
+        database = TestDatabase.createReplacingNewPipeDatabase()
-            ApplicationProvider.getApplicationContext(),
-            AppDatabase::class.java
-        )
-            .allowMainThreadQueries()
-            .build()
-
         manager = LocalPlaylistManager(database)
     }
 

app/src/androidTest/java/org/schabi/newpipe/testUtil/TestDatabase.kt

@@ -0,0 +1,32 @@
+package org.schabi.newpipe.testUtil
+
+import androidx.room.Room
+import androidx.test.core.app.ApplicationProvider
+import org.junit.Assert.assertSame
+import org.schabi.newpipe.NewPipeDatabase
+import org.schabi.newpipe.database.AppDatabase
+
+class TestDatabase {
+    companion object {
+        fun createReplacingNewPipeDatabase(): AppDatabase {
+            val database = Room.inMemoryDatabaseBuilder(
+                ApplicationProvider.getApplicationContext(),
+                AppDatabase::class.java
+            )
+                .allowMainThreadQueries()
+                .build()
+
+            val databaseField = NewPipeDatabase::class.java.getDeclaredField("databaseInstance")
+            databaseField.isAccessible = true
+            databaseField.set(NewPipeDatabase::class, database)
+
+            assertSame(
+                "Mocking database failed!",
+                database,
+                NewPipeDatabase.getInstance(ApplicationProvider.getApplicationContext())
+            )
+
+            return database
+        }
+    }
+}