Extract export database logic into own class

- Separate it from the UI.
- Add happy path unit test.

app/src/test/java/org/schabi/newpipe/settings/ContentSettingsManagerTest.kt

@@ -0,0 +1,72 @@
+package org.schabi.newpipe.settings
+
+import android.content.SharedPreferences
+import org.junit.Assert
+import org.junit.Assume
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.Suite
+import org.mockito.Mockito
+import org.mockito.Mockito.`when`
+import org.mockito.junit.MockitoJUnitRunner
+import org.schabi.newpipe.settings.ContentSettingsManagerTest.ExportTest
+import java.io.File
+import java.io.ObjectInputStream
+import java.util.zip.ZipFile
+
+@RunWith(Suite::class)
+@Suite.SuiteClasses(ExportTest::class)
+class ContentSettingsManagerTest {
+
+    @RunWith(MockitoJUnitRunner::class)
+    class ExportTest {
+
+        private lateinit var preferences: SharedPreferences
+        private lateinit var newpipeDb: File
+        private lateinit var newpipeSettings: File
+
+        @Before
+        fun beforeClass() {
+
+            val dbPath = javaClass.classLoader?.getResource("settings/newpipe.db")?.file
+            val settingsPath = javaClass.classLoader?.getResource("settings/newpipe.settings")?.path
+            Assume.assumeNotNull(dbPath)
+            Assume.assumeNotNull(settingsPath)
+
+            newpipeDb = File(dbPath!!)
+            newpipeSettings = File(settingsPath!!)
+        }
+
+        @Before
+        fun before() {
+            preferences = Mockito.mock(SharedPreferences::class.java, Mockito.withSettings().stubOnly())
+        }
+
+        @Test
+        fun `The settings must be exported successfully in the correct format`() {
+            val expectedPreferences = mapOf("such pref" to "much wow")
+            `when`(preferences.all).thenReturn(expectedPreferences)
+
+            val manager = ContentSettingsManager(newpipeDb, newpipeSettings)
+
+            val output = File.createTempFile("newpipe_", "")
+            manager.exportDatabase(preferences, output.absolutePath)
+
+            val zipFile = ZipFile(output.absoluteFile)
+            val entries = zipFile.entries().toList()
+            Assert.assertEquals(2, entries.size)
+
+            zipFile.getInputStream(entries.first { it.name == "newpipe.db" }).use { actual ->
+                newpipeDb.inputStream().use { expected ->
+                    Assert.assertEquals(expected.reader().readText(), actual.reader().readText())
+                }
+            }
+
+            zipFile.getInputStream(entries.first { it.name == "newpipe.settings" }).use { actual ->
+                val actualPreferences = ObjectInputStream(actual).readObject()
+                Assert.assertEquals(expectedPreferences, actualPreferences)
+            }
+        }
+    }
+}