diff --git a/tests/testthat/test-serp.R b/tests/testthat/test-serp.R
index fbe5b3932..9d63cef40 100644
--- a/tests/testthat/test-serp.R
+++ b/tests/testthat/test-serp.R
@@ -28,6 +28,45 @@ test_that("get_df", {
 })
 
 
+test_that("get_modelmatrix", {
+  expect_identical(
+    get_modelmatrix(m1),
+    structure(
+      c(
+        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+        0, 0, 0, 0, 1, 1, 1, 1,
+        0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1,
+        1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0,
+        0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1,
+        1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1,
+        0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0,
+        0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0,
+        1, 1, 0, 0, 1, 1, 0, 0, 1, 1
+      ),
+      dim = c(72L, 3L),
+      dimnames = list(
+        c(
+          "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11",
+          "12", "13", "14", "15", "16", "17", "18", "19", "20", "21",
+          "22", "23", "24", "25", "26", "27", "28", "29", "30", "31",
+          "32", "33", "34", "35", "36", "37", "38", "39", "40", "41",
+          "42", "43", "44", "45", "46", "47", "48", "49", "50", "51",
+          "52", "53", "54", "55", "56", "57", "58", "59", "60", "61",
+          "62", "63", "64", "65", "66", "67", "68", "69", "70", "71",
+          "72"
+        ),
+        c("(Intercept)", "tempwarm", "contactyes")
+      ),
+      assign = 0:2,
+      contrasts = list(temp = "contr.treatment", contact = "contr.treatment")
+    ),
+    ignore_attr = TRUE
+  )
+})
+
+
 test_that("find_predictors", {
   expect_identical(find_predictors(m1), list(conditional = c("temp", "contact")))
   expect_identical(find_predictors(m1, flatten = TRUE), c("temp", "contact"))