private fun Snapshot.assertValue(
    index: Int,
    value: String,
  ) {
    getSource(index).use { source ->
      assertThat(sourceAsString(source)).isEqualTo(value)
      assertThat(getLength(index)).isEqualTo(value.length.toLong())
    }
  }

  private fun sourceAsString(source: Source) = source.buffer().readUtf8()

  private fun Editor.assertInoperable() {
    assertFailsWith<IllegalStateException> {