diff --git a/tests/testthat/test-mutate.R b/tests/testthat/test-mutate.R
new file mode 100644
index 00000000..fc994155
--- /dev/null
+++ b/tests/testthat/test-mutate.R
@@ -0,0 +1,25 @@
+test_that("mutate works", {
+    skip_if_not_installed("outbreaks")
+
+    data(ebola_sim_clean, package = "outbreaks")
+    dat <-
+        ebola_sim_clean$linelist |>
+        subset(!is.na(hospital)) |>
+        incidence_(date_of_onset, hospital, interval = "isoweek")
+
+    expect_identical(
+        as_tibble(
+            mutate(
+                dat,
+                ave = data.table::frollmean(count, n = 3L, align = "right")
+            )
+        ),
+
+        mutate(
+            as_tibble(dat),
+            ave = data.table::frollmean(count, n = 3L, align = "right"),
+            .by = c(count_variable, hospital)
+        )
+    )
+
+})
diff --git a/tests/testthat/test-nest.R b/tests/testthat/test-nest.R
new file mode 100644
index 00000000..6dfb25cf
--- /dev/null
+++ b/tests/testthat/test-nest.R
@@ -0,0 +1,13 @@
+test_that("nest works", {
+    skip_if_not_installed("outbreaks")
+    data(ebola_sim_clean, package = "outbreaks")
+    dat <-
+        ebola_sim_clean$linelist |>
+        subset(!is.na(hospital)) |>
+        incidence_(date_of_onset, hospital, interval = "isoweek")
+
+    expect_identical(
+        nest(dat),
+        nest(as_tibble(dat), .by = c(count_variable, hospital))
+    )
+})
diff --git a/tests/testthat/test-split.R b/tests/testthat/test-split.R
new file mode 100644
index 00000000..777c3787
--- /dev/null
+++ b/tests/testthat/test-split.R
@@ -0,0 +1,17 @@
+test_that("split works", {
+    skip_if_not_installed("outbreaks")
+
+    data(ebola_sim_clean, package = "outbreaks")
+
+    dat <-
+        ebola_sim_clean$linelist |>
+        subset(!is.na(hospital)) |>
+        incidence_(date_of_onset, hospital, interval = "isoweek")
+
+    out <- split(dat)
+
+    expected <- vctrs::vec_split(as_tibble(dat), as_tibble(dat)[c("count_variable", "hospital")])
+
+    expect_identical(c(out), expected$val)
+    expect_identical(attr(out, "key"), expected$key)
+})
diff --git a/tests/testthat/test-summarise.R b/tests/testthat/test-summarise.R
new file mode 100644
index 00000000..720d7371
--- /dev/null
+++ b/tests/testthat/test-summarise.R
@@ -0,0 +1,14 @@
+test_that("summarise works", {
+    skip_if_not_installed("outbreaks")
+
+    data(ebola_sim_clean, package = "outbreaks")
+    dat <-
+        ebola_sim_clean$linelist |>
+        subset(!is.na(hospital)) |>
+        incidence_(date_of_onset, hospital, interval = "isoweek")
+
+    expect_identical(
+        summarise(dat, sum(count)),
+        summarise(as_tibble(dat), sum(count), .by = c(count_variable, hospital))
+    )
+})