skip_if_not_installed("survival")

Surv <- survival::Surv
strata <- survival::strata

f1 <- as.formula("Surv(time, status) ~ strata(sex) * x + x2")
f2 <- as.formula("Surv(time, status) ~ x * strata(sex) * x2")
f3 <- as.formula("Surv(time, status) ~ x + x2 * strata(sex)")
f4 <- as.formula("Surv(time, status) ~ strata(sex) + x + x2")
f5 <- as.formula("Surv(time, status) ~ x * strata(sex) + x2")
f6 <- as.formula("Surv(time, status) ~ x + x2 + strata(sex)")

dat <- list(
  time = c(4, 3, 1, 1, 2, 2, 3),
  status = c(1, 1, 1, 0, 1, 1, 0),
  x = c(0, 2, 1, 1, 1, 0, 0),
  x2 = c(0, 2, 1, 0, 1, 1, 0),
  sex = c(0, 0, 0, 0, 1, 1, 1)
)

test_that("find_predictors strata1", {
  mod <- suppressWarnings(survival::coxph(f1, data = dat, ties = "breslow"))
  expect_equal(find_predictors(mod), list(conditional = c("x", "x2"), strata = "sex"))
})

test_that("find_predictors strata2", {
  mod <- suppressWarnings(survival::coxph(f2, data = dat, ties = "breslow"))
  expect_equal(find_predictors(mod), list(conditional = c("x", "x2"), strata = "sex"))
})

test_that("find_predictors strata3", {
  mod <- suppressWarnings(survival::coxph(f3, data = dat, ties = "breslow"))
  expect_equal(find_predictors(mod), list(conditional = c("x", "x2"), strata = "sex"))
})

test_that("find_predictors strata4", {
  mod <- suppressWarnings(survival::coxph(f4, data = dat, ties = "breslow"))
  expect_equal(find_predictors(mod), list(conditional = c("x", "x2"), strata = "sex"))
})

test_that("find_predictors strata5", {
  mod <- suppressWarnings(survival::coxph(f5, data = dat, ties = "breslow"))
  expect_equal(find_predictors(mod), list(conditional = c("x", "x2"), strata = "sex"))
})

test_that("find_predictors strata6", {
  mod <- suppressWarnings(survival::coxph(f6, data = dat, ties = "breslow"))
  expect_equal(find_predictors(mod), list(conditional = c("x", "x2"), strata = "sex"))
})