test_push_row <- function(){
  wide_df = data.frame(
    subj = c("Tom", "Mary", "Jack"),
    t0 = c( 50, 42, 80),
    t1 = c( 48, 42, 75),
    t2 = c( 46, 44, 72),
    t3 = c( 42, 42, 73)
  )

  code = "
    subject = subj
    time = 0
    bw = t0
    push!()

    time = 1
    bw = t1 
    push!()

    time = 2
    bw = t2
    push!()

    time = 3
    bw = t3
  "

  long_df = datasailr::sail(wide_df , code = code, fullData=FALSE)
  tom_long_df = long_df[long_df$subject=="Tom", ]

  RUnit::checkEqualsNumeric( 4 * nrow(wide_df), nrow(long_df))
  RUnit::checkEqualsNumeric( tom_long_df$bw , c(50, 48, 46, 42))

}
