diff --git a/tests/testthat/test-testThenRank.R b/tests/testthat/test-testThenRank.R
new file mode 100644
index 0000000..6c642c4
--- /dev/null
+++ b/tests/testthat/test-testThenRank.R
@@ -0,0 +1,16 @@
+test_that("test-then-rank raises warning for one case", {
+  data <- rbind(
+    data.frame(algo="A1", value=0.6, case="C1"),
+    data.frame(algo="A2", value=0.8, case="C1"))
+
+  challenge <- as.challenge(data, taskName="T1", algorithm="algo", case="case", value="value", smallBetter = TRUE)
+
+  expect_warning(ranking <- challenge%>%testThenRank(),
+                 "Only one case in task.", fixed = TRUE)
+
+  expectedRanking <- rbind(
+    "A1" = data.frame(prop_significance = 0, rank = 1),
+    "A2" = data.frame(prop_significance = 0, rank = 1))
+
+  expect_equal(ranking$matlist$T1, expectedRanking)
+})