
  set.seed(1)
  DF <- data.frame("Y" = rnorm(100))
  DF$D <- ifelse(DF$Y > 0, 1, 0)


  # compute group-specific sample means of `Y`
  
  
  # regress `Y` on `D`


   mu_Y_D1 <- mean(DF$Y[DF$D ==1])
   mu_Y_D0 <- mean(DF$Y[DF$D ==0])
   lm(Y ~ D, data = DF)


  test_object("mu_Y_D1")
  test_object("mu_Y_D1")
  test_or(
  {
  test_function("lm", args = "formula")
  },{
  ex() %>% override_solution("lm(DF$Y ~ DF$D)") %>% check_function("lm") %>% check_arg("formula")
  }
  )