Timing of expect() #Chisel3 Tester - chisel

Question

I would like to confirm that timing of the iotester of chisel3. I have long time did not touch the iotester, and now I do the testing. Then I confused the timing of the output on expect().
For example;
val reg = RegInit(Bool(), false.B)
...
reg = !io.input
io.output = reg
This can be tested by iotester as follows;
poke(c.io.input, 0)
step(1)
expect(c.io.output, 0)//Latch the input on reg
step(1)
expect(c.io.output, 1)//Output the reg
Is my understanding correct?
--
NaN

Answer 1

Not quite. Here's a filled out example
import chisel3._
import chiseltest._
import chiseltest.ChiselScalatestTester
import org.scalatest.FreeSpec
class Toggle extends MultiIOModule {
val in = IO(Input(Bool()))
val out = IO(Output(Bool()))
val reg = RegInit(false.B)
reg := ! in
out := reg
}
class ToggleTester extends FreeSpec with ChiselScalatestTester {
"test toggle" in {
test(new Toggle()) { c =>
c.in.poke(false.B) // clock is low
c.out.expect(false.B) // clock stil low, reg still at initial value
c.clock.step() // clock goes high
c.out.expect(true.B) // register has toggled
}
}
}
pokes take place when the clock has just gone low.
BTW, this example is using the new chiseltest test harness. I recommend using it over the older chisel-iotesters.