Don't use "if" inside for comprehensions involving Futures thinking they work like sequences

FutMain.scala

import scala.concurrent.{ Await, Future }
import scala.concurrent.duration._
import scala.concurrent.ExecutionContext.Implicits.global

object FutMain {
  def main(args: Array[String]): Unit = {
    val part1 = (1 to 3).map(successful)
    val part2 = Seq(iffed(4))
    val part3 = (5 to 7).map(successful)
    val total = Future.sequence(part1 ++ part2 ++ part3)
    val res = Await.result(total, 1.minute)
    println(res)
  }

  def successful(i: Int): Future[Int] = Future.successful(i)
  def iffed(i: Int): Future[Int] =
    for {
      testMe <- Future.successful(i)
      if testMe > 1000
    } yield 0
}

This will give you

[error] (run-main-4) java.util.NoSuchElementException: Future.filter predicate is not satisfied
java.util.NoSuchElementException: Future.filter predicate is not satisfied