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


      # calcular las medias muestrales específicas del grupo de "Y"
      
      # regreso `Y` en `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")
      }
      )