Add tests for migrations in the Room database

Doing this increase the level of reliability of migrations, as we can be
pretty much more confident of avoiding problems with them.

app/build.gradle

@@ -84,6 +84,10 @@ android {
     androidExtensions {
         experimental = true
     }
+
+    sourceSets {
+        androidTest.assets.srcDirs += files("$projectDir/schemas".toString())
+    }
 }
 
 ext {
@@ -100,6 +104,8 @@ ext {
 dependencies {
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
 
+    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
+    androidTestImplementation "android.arch.persistence.room:testing:1.1.1"
     androidTestImplementation('androidx.test.espresso:espresso-core:3.1.0', {
         exclude module: 'support-annotations'
     })

app/src/androidTest/java/org/schabi/newpipe/database/AppDatabaseTest.kt

@@ -0,0 +1,79 @@
+package org.schabi.newpipe.database
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import androidx.room.Room
+import androidx.room.testing.MigrationTestHelper
+import androidx.sqlite.db.framework.FrameworkSQLiteOpenHelperFactory
+import androidx.test.core.app.ApplicationProvider
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import androidx.test.platform.app.InstrumentationRegistry
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.schabi.newpipe.extractor.stream.StreamType
+
+@RunWith(AndroidJUnit4::class)
+class AppDatabaseTest {
+    companion object {
+        private const val DEFAULT_SERVICE_ID = 0
+        private const val DEFAULT_URL = "https://www.youtube.com/watch?v=cDphUib5iG4"
+        private const val DEFAULT_TITLE = "Test Title"
+        private val DEFAULT_TYPE = StreamType.VIDEO_STREAM
+        private const val DEFAULT_DURATION = 480L
+        private const val DEFAULT_UPLOADER_NAME = "Uploader Test"
+        private const val DEFAULT_THUMBNAIL = "https://example.com/example.jpg"
+    }
+
+    @get:Rule val testHelper = MigrationTestHelper(InstrumentationRegistry.getInstrumentation(),
+            AppDatabase::class.java.canonicalName, FrameworkSQLiteOpenHelperFactory());
+
+    @Test
+    fun migrateDatabaseFrom2to3() {
+        val databaseInV2 = testHelper.createDatabase(AppDatabase.DATABASE_NAME, Migrations.DB_VER_2)
+
+        databaseInV2.run {
+            insert("streams", SQLiteDatabase.CONFLICT_FAIL, ContentValues().apply {
+                // put("uid", null)
+                put("service_id", DEFAULT_SERVICE_ID)
+                put("url", DEFAULT_URL)
+                put("title", DEFAULT_TITLE)
+                put("stream_type", DEFAULT_TYPE.name)
+                put("duration", DEFAULT_DURATION)
+                put("uploader", DEFAULT_UPLOADER_NAME)
+                put("thumbnail_url", DEFAULT_THUMBNAIL)
+            })
+            close()
+        }
+
+        testHelper.runMigrationsAndValidate(AppDatabase.DATABASE_NAME, Migrations.DB_VER_3,
+                true, Migrations.MIGRATION_2_3);
+
+        val migratedDatabaseV3 = getMigratedDatabase()
+        val listFromDB = migratedDatabaseV3.streamDAO().all.blockingFirst()
+        assertEquals(1, listFromDB.size)
+
+        val streamFromMigratedDatabase = listFromDB.first()
+        assertEquals(DEFAULT_SERVICE_ID, streamFromMigratedDatabase.serviceId)
+        assertEquals(DEFAULT_URL, streamFromMigratedDatabase.url)
+        assertEquals(DEFAULT_TITLE, streamFromMigratedDatabase.title)
+        assertEquals(DEFAULT_TYPE, streamFromMigratedDatabase.streamType)
+        assertEquals(DEFAULT_DURATION, streamFromMigratedDatabase.duration)
+        assertEquals(DEFAULT_UPLOADER_NAME, streamFromMigratedDatabase.uploader)
+        assertEquals(DEFAULT_THUMBNAIL, streamFromMigratedDatabase.thumbnailUrl)
+        assertNull(streamFromMigratedDatabase.viewCount)
+        assertNull(streamFromMigratedDatabase.textualUploadDate)
+        assertNull(streamFromMigratedDatabase.uploadDate)
+        assertNull(streamFromMigratedDatabase.isUploadDateApproximation)
+    }
+
+    private fun getMigratedDatabase(): AppDatabase {
+        val database: AppDatabase = Room.databaseBuilder(ApplicationProvider.getApplicationContext(),
+                AppDatabase::class.java, AppDatabase.DATABASE_NAME)
+                .build()
+        testHelper.closeWhenFinished(database)
+        return database
+    }
+}