diff --git a/ana/prediction_test.go b/ana/prediction_test.go
index 3921449..454b8b4 100644
--- a/ana/prediction_test.go
+++ b/ana/prediction_test.go
@@ -43,6 +43,9 @@ func TestPredictionPredict(t *testing.T) {
 		"empty": {
 			want: ledger.Register{theseK: {}},
 		},
+		"double": {
+			prediction: {double},
+		},
 	}
 
 	for name, d := range cases {