test_that("correct calculations when you edit options on times and round trip", {
  expect_equal(4*rail_emissions("Southampton Central", "Manchester Piccadilly"), rail_emissions("Southampton Central", "Manchester Piccadilly", round_trip = TRUE, times_journey = 2))
})

test_that("Adding a via puts it in at the correct point (centre of journey, not end)", {
  expect_equal(rail_emissions("Southampton Central", "Manchester Piccadilly", "Reading"), c(rail_emissions("Southampton Central", "Reading") + rail_emissions("Reading", "Manchester Piccadilly")))
})

test_that("incorrect values gives error", {
  expect_error(rail_emissions(from = "Southampton", to = "Manchester Piccadilly"))
  expect_error(rail_emissions(from = "Southampton Central", to = "manchester piccadilly"))
  expect_error(rail_emissions(from = "Southampton Central", to = "Paddington", via = c("Readng")))
})