diff --git a/tests/triacontagon/test_cumcount.py b/tests/triacontagon/test_cumcount.py
new file mode 100644
index 0000000..b9a8780
--- /dev/null
+++ b/tests/triacontagon/test_cumcount.py
@@ -0,0 +1,26 @@
+from triacontagon.cumcount import dfill, \
+    argunsort, \
+    cumcount
+import numpy as np
+
+
+def test_dfill_01():
+    input = np.array([1, 1, 1, 1, 1, 2, 2, 3, 3, 3, 4, 4, 5, 5])
+    output = dfill(input)
+    expected = np.array([0, 0, 0, 0, 0, 5, 5, 7, 7, 7, 10, 10, 12, 12])
+    assert np.all(output == expected)
+
+
+def test_argunsort_01():
+    input = np.array([1, 1, 2, 3, 3, 4, 1, 1, 5, 5, 2, 3, 1, 4])
+    output = np.argsort(input, kind='mergesort')
+    output = argunsort(output)
+    expected = np.array([0, 1, 5, 7, 8, 10, 2, 3, 12, 13, 6, 9, 4, 11])
+    assert np.all(output == expected)
+
+
+def test_cumcount_01():
+    input = np.array([1, 1, 2, 3, 3, 4, 1, 1, 5, 5, 2, 3, 1, 4])
+    output = cumcount(input)
+    expected = np.array([0, 1, 0, 0, 1, 0, 2, 3, 0, 1, 1, 2, 4, 1])
+    assert np.all(output == expected)