diff --git a/pbxplore/test/test_functions.py b/pbxplore/test/test_functions.py
index 7b68276..05500f1 100644
--- a/pbxplore/test/test_functions.py
+++ b/pbxplore/test/test_functions.py
@@ -216,7 +216,7 @@ def test_make_profile_partial(self):
                      'ghijkl', 'hijklm', 'ijklmn',
                      'ghijkl', 'hijklm', 'ijklmn',
                      'jklmno', 'klmnop',            # ignore in the test
-                     'ijklmn']          
+                     'ijklmn']
         # Using 10 sequences makes things easier
         indices = [0, 1, 2, 6, 7, 8, 9, 10, 11, 14]
         ref_profile = numpy.array([[0.1, 0.0, 0.0, 0.0, 0.0, 0.0],   # a
@@ -238,5 +238,16 @@ def test_make_profile_partial(self):
         profile = kmeans.make_profile_partial(sequences, indices)
         assert(numpy.allclose(ref_profile, profile))
 
+    def test_argmax(self):
+        reference = (([0, 1, 2, 3, 4], 4),  # Ordered
+                     ([4, 3, 2, 1, 0], 0),  # Reverse ordered
+                     ([1, 3, 2, 4, 0], 3),  # Random order
+                     ([0, 0, 3, 4, 4], 3),  # Duplicates
+                     ([4, 4, 4, 4, 4], 0),  # All the same
+                     )
+        for test_case, expectation in reference:
+            self.assertEqual(kmeans._argmax(test_case), expectation)
+
+
 if __name__ == '__main__':
     unittest.main()