test_that("get_fit returns underlying lm model", {
  
  dat <- data.frame(
    x = 1:20,
    y = 2 + 3 * (1:20) + rnorm(20)
  )
  
  m <- fit_biomix(
    y ~ x,
    data = dat
  )
  
  fit <- get_fit(m)
  
  expect_true(inherits(fit, "lm"))
})

test_that("get_fit works for ordinary BioMixModel", {
  
  m <- fit_biomix(
    y ~ x,
    data.frame(
      y = rnorm(20),
      x = rnorm(20)
    )
  )
  
  expect_s3_class(get_fit(m), "lm")
})

# ---------------------------------------------------------
# Invalid object
# ---------------------------------------------------------

test_that("get_fit rejects non-BioMixModel objects", {
  
  expect_error(
    get_fit(lm(y ~ x, data = data.frame(
      y = rnorm(10),
      x = rnorm(10)
    ))),
    "model must be a BioMixModel object"
  )
  
  expect_error(
    get_fit(list(fit = "something")),
    "model must be a BioMixModel object"
  )
  
  expect_error(
    get_fit(NULL),
    "model must be a BioMixModel object"
  )
})


# ---------------------------------------------------------
# Fallback to fixed component
# ---------------------------------------------------------

test_that("get_fit returns fixed component when fit is NULL", {
  
  m <- structure(
    list(
      fit = NULL,
      fixed = c(
        intercept = 2,
        slope = 3
      )
    ),
    class = c("biomix_test", "biomix")
  )
  
  result <- get_fit(m)
  
  expect_equal(
    result,
    c(
      intercept = 2,
      slope = 3
    )
  )
  
  expect_type(result, "double")
})


# ---------------------------------------------------------
# No fitted model available
# ---------------------------------------------------------

test_that("get_fit errors when fit and fixed are both unavailable", {
  
  m <- structure(
    list(
      fit = NULL,
      fixed = NULL
    ),
    class = "biomix"
  )
  
  expect_error(
    get_fit(m),
    "No fitted model found"
  )
})


# ---------------------------------------------------------
# Missing fit component
# ---------------------------------------------------------

test_that("get_fit errors when no fit component exists", {
  
  m <- structure(
    list(
      fixed = NULL
    ),
    class = "biomix"
  )
  
  expect_error(
    get_fit(m),
    "No fitted model found"
  )
})


# ---------------------------------------------------------
# Missing fixed component
# ---------------------------------------------------------

test_that("get_fit errors when fit and fixed are missing", {
  
  m <- structure(
    list(),
    class = "biomix"
  )
  
  expect_error(
    get_fit(m),
    "No fitted model found"
  )
})

get_fit <- function(model) {
  
  if (!inherits(model, "biomix")) {
    stop("model must be a BioMixModel object.", call. = FALSE)
  }
  
  if (!is.null(model$fit)) {
    return(model$fit)
  }
  
  if (!is.null(model$fixed)) {
    return(model$fixed)
  }
  
  stop("No fitted model found.", call. = FALSE)
}
# ---------------------------------------------------------
# Invalid object
# ---------------------------------------------------------

test_that("get_fit rejects non-BioMixModel objects", {
  
  expect_error(
    get_fit(lm(y ~ x, data = data.frame(
      y = rnorm(10),
      x = rnorm(10)
    ))),
    "model must be a BioMixModel object"
  )
  
  expect_error(
    get_fit(list(fit = "something")),
    "model must be a BioMixModel object"
  )
  
  expect_error(
    get_fit(NULL),
    "model must be a BioMixModel object"
  )
})


# ---------------------------------------------------------
# Fallback to fixed component
# ---------------------------------------------------------

test_that("get_fit returns fixed component when fit is NULL", {
  
  m <- structure(
    list(
      fit = NULL,
      fixed = c(
        intercept = 2,
        slope = 3
      )
    ),
    class = c("biomix_test", "biomix")
  )
  
  result <- get_fit(m)
  
  expect_equal(
    result,
    c(
      intercept = 2,
      slope = 3
    )
  )
  
  expect_type(result, "double")
})


# ---------------------------------------------------------
# No fitted model available
# ---------------------------------------------------------

test_that("get_fit errors when fit and fixed are both unavailable", {
  
  m <- structure(
    list(
      fit = NULL,
      fixed = NULL
    ),
    class = "biomix"
  )
  
  expect_error(
    get_fit(m),
    "No fitted model found"
  )
})


# ---------------------------------------------------------
# Missing fit component
# ---------------------------------------------------------

test_that("get_fit errors when no fit component exists", {
  
  m <- structure(
    list(
      fixed = NULL
    ),
    class = "biomix"
  )
  
  expect_error(
    get_fit(m),
    "No fitted model found"
  )
})


# ---------------------------------------------------------
# Missing fixed component
# ---------------------------------------------------------

test_that("get_fit errors when fit and fixed are missing", {
  
  m <- structure(
    list(),
    class = "biomix"
  )
  
  expect_error(
    get_fit(m),
    "No fitted model found"
  )
})