--- a/test/rps3_tests.erl	Sat Mar 08 23:37:19 2014 +0900
+++ b/test/rps3_tests.erl	Sat Mar 08 23:40:26 2014 +0900
@@ -12,3 +12,7 @@
     ?assertEqual(undefined, rps3:winning_hand([rock, paper, scissors])),
     ?assertEqual(paper,     rps3:winning_hand([rock, paper, paper])),
     ?assertEqual(paper,     rps3:winning_hand([rock, rock, paper])).
+
+why_test() ->
+    ?assertEqual("crushes", rps3:why(rock, scissors)),
+    ?assertEqual("paper covers rock", rps3:why(paper, [rock])).

--- a/test/rps5_tests.erl	Sat Mar 08 23:37:19 2014 +0900
+++ b/test/rps5_tests.erl	Sat Mar 08 23:40:26 2014 +0900
@@ -12,3 +12,7 @@
     ?assertEqual(undefined, rps5:winning_hand([rock, paper, scissors])),
     ?assertEqual(paper,     rps5:winning_hand([rock, paper, paper])),
     ?assertEqual(paper,     rps5:winning_hand([rock, rock, paper])).
+
+why_test() ->
+    ?assertEqual("smashes", rps5:why(spock, scissors)),
+    ?assertEqual("lizard poisons spock, eats paper", rps5:why(lizard, [spock, paper])).