diff --git a/tests/testthat/test-scale-gradient.R b/tests/testthat/test-scale-gradient.R
index fafa2226fe..140c4027c8 100644
--- a/tests/testthat/test-scale-gradient.R
+++ b/tests/testthat/test-scale-gradient.R
@@ -9,3 +9,76 @@ test_that("points outside the limits are plotted as NA", {
   correct_fill <- c("#B26D65", "#DCB4AF", "orange")
   expect_equal(layer_data(p)$fill, correct_fill)
 })
+
+
+test_that("scale_params mapping_method supports binned", {
+  sc <- scale_fill_continuous()
+  x <- seq(0, 1, length.out = 10)
+  only_two <- sc$map(x, limits = c(0, 1), scale_params = list(mapping_method = "binned", mapping_method_bins = 2))
+  expect_equal(length(unique(only_two)), 2L)
+})
+
+test_that("palette with accepts_native_output returns native colours", {
+  sc <- scale_fill_continuous()
+  sc$palette <- structure(
+    function(x, color_fmt = "character") {
+      if (color_fmt == "character") {
+        rep("red", length(x))
+      } else {
+        rep(-16776961L, length(x))
+      }
+    },
+    accepts_native_output = TRUE
+  )
+  x <- 0.5
+  nat <- sc$map(x, limits = c(0, 1), scale_params = list(color_fmt = "native"))
+  expect_equal(nat, -16776961L)
+  chr <- sc$map(x, limits = c(0, 1), scale_params = list(color_fmt = "character"))
+  expect_equal(chr, "red")
+  chr2 <- sc$map(x, limits = c(0, 1))
+  expect_equal(chr, chr2)
+})
+
+test_that("palette without accepts_native_output returns native colours as well", {
+  sc <- scale_fill_continuous()
+  sc$palette <- function(x) {
+    rep("red", length(x))
+  }
+  x <- 0.5
+  nat <- sc$map(x, limits = c(0, 1), scale_params = list(color_fmt = "native"))
+  expect_equal(nat, -16776961L)
+  chr <- sc$map(x, limits = c(0, 1), scale_params = list(color_fmt = "character"))
+  expect_equal(chr, "red")
+  chr2 <- sc$map(x, limits = c(0, 1))
+  expect_equal(chr, chr2)
+})
+
+
+test_that("palette with may_return_NA=FALSE works as expected", {
+  sc <- scale_fill_continuous()
+  # A palette that may return NAs, will have NAs replaced by the scale's na.value
+  # by the scale:
+  sc$palette <- structure(
+    function(x) {
+      rep(NA_character_, length(x))
+    },
+    may_return_NA = TRUE
+  )
+  sc$na.value <- "red"
+  nat <- sc$map(0.5, limits = c(0, 1))
+  expect_equal(nat, "red")
+
+  # This palette is lying, because it returns NA even though it says it can't.
+  # The scale will not replace the NA values, leading to further errors.
+  # You should not do this in production, but it helps to test:
+  sc <- scale_fill_continuous()
+  sc$palette <- structure(
+    function(x) {
+      rep(NA_character_, length(x))
+    },
+    may_return_NA = FALSE
+  )
+  sc$na.value <- "red"
+  nat <- sc$map(0.5, limits = c(0, 1))
+  expect_equal(nat, NA_character_)
+})