## Test `fderiv()` function

## load packages
library("testthat")
library("gratia")
library("mgcv")

mod <- gam(y ~ s(x0) + s(x1) + fac, data = su_eg4, method = "REML")

test_that("fderiv is deprecated", {
    skip_on_cran()
    skip_on_ci()
    withr::local_options(digits = 3)
    expect_snapshot(fderiv(mod))
})

test_that("fderiv() can create newdata with factors in model", {
    withr::local_options(lifecycle_verbosity = "quiet")
    ## Example from https://github.com/scottkosty/tsgam/commit/a964ef3fcfc6847f737bd54e4d831b97d9d8b280
    fd <- fderiv(mod)                   # shouldn't thrown an error
    expect_s3_class(fd, "fderiv")
})

test_that("fderiv() can handle factors in user-supplied newdata", {
    withr::local_options(lifecycle_verbosity = "quiet")
    ## Example from https://github.com/scottkosty/tsgam/commit/80293d4887ef322686d056ad54dcd183cdab0966
    newd <- delete_response(mod, su_eg4)
    expect_silent(fd <- fderiv(mod, newdata = su_eg4))
    expect_s3_class(fd, "fderiv")
})

test_that("fderiv() can handle offsets", {
    withr::local_options(lifecycle_verbosity = "quiet")
    ## Example from https://github.com/scottkosty/tsgam/commit/80293d4887ef322686d056ad54dcd183cdab0966
    mod <- gam(y ~ fac + s(x1) + offset(x0), data = su_eg4,
               method = "REML")
    expect_silent(fd <- fderiv(mod))
    expect_s3_class(fd, "fderiv")
    expect_silent(fd <- fderiv(mod, newdata = su_eg4))
    expect_s3_class(fd, "fderiv")
})