Pure doobie Transactor for mocking ConnectionIO

pure_transactor.scala

// https://github.com/tpolecat/doobie/issues/460

object Test {

  import cats.implicits._
  import cats.effect.IO
  import cats.effect.unsafe.implicits.global
  import doobie.{ConnectionIO, Transactor}
  import doobie.implicits._

  val u      = ().pure[ConnectionIO]
  val s      = doobie.util.transactor.Strategy(u, u, u, u)
  val noopXa = Transactor.fromConnection[IO](null).copy(strategy0 = s)

  val value: ConnectionIO[Int] = 42.pure[ConnectionIO]

  val r = value.transact(noopXa).unsafeRunSync()
}

Test.r // 42