test_that("maybe modifies a function to return a maybe value", {
  for_all(
    a = anything(),
    property = function(a) maybe(identity)(a) %>% is_maybe() %>% expect_true()
  )
})

test_that("maybe modifies a function to return a just value", {
  for_all(
    a = anything(),
    property = function(a) maybe(identity)(a) %>% is_just() %>% expect_true()
  )
})

test_that("maybe modifies a function to return nothing when it has warnings", {
  for_all(
    a = anything(),
    property = function(a)
      maybe(function(b) warning(""))(a) %>%
        is_nothing() %>%
        expect_true()
  )
})

test_that("maybe modifies a function to return nothing when it has errors", {
  for_all(
    a = anything(),
    property = function(a)
      maybe(function(b) stop(""))(a) %>%
        is_nothing() %>%
        expect_true()
  )
})

test_that("allow_warning allows functions with warnings to return just", {
  for_all(
    a = anything(),
    property = function(a)
      maybe(function(a) { warning(""); a }, allow_warning = TRUE)(a) %>%
        is_just() %>%
        expect_true()
  )
})

test_that("maybe will return a just value if the predicate returns TRUE", {
  for_all(
    a = any_atomic(),
    property = function(a)
      maybe(identity, ensure = is.atomic)(a) %>%
        is_just() %>%
        expect_true()
  )
})

test_that("maybe will return nothing if the predicate returns FALSE", {
  for_all(
    a = any_undefined(),
    property = function(a)
      maybe(identity, ensure = not_undefined)(a) %>%
        is_nothing() %>%
        expect_true()
  )
})