A non-working test with LiveData

PostDaoTest.kt

@RunWith(AndroidJUnit4::class)
class PostDaoReadWriteTest {
    private lateinit var postDao: PostDao
    private lateinit var db: TestDatabase

    @Before
    fun createDb() {
        val context = ApplicationProvider.getApplicationContext<Context>()
        db = Room.inMemoryDatabaseBuilder(
                context, TestDatabase::class.java).build()
        postDao = db.getPostDao()
    }

    @After
    @Throws(IOException::class)
    fun closeDb() {
        db.close()
    }

    @Test
    @Throws(Exception::class)
    fun writePostAndReadInList() {
        assertEquals(0, postDao.getAll().value?.size)
        val post = TestUtil.createPost(id=42)
        postDao.insert(post)
        assertEquals(1, posttDao.getAll().value?.size)
    }
}