diff --git a/internal/2025/DayNine/code_test.go b/internal/2025/DayNine/code_test.go
new file mode 100644
index 0000000..1185233
--- /dev/null
+++ b/internal/2025/DayNine/code_test.go
@@ -0,0 +1,22 @@
+package daynine
+
+import "testing"
+
+var testInput = []string{
+	"7,1",
+	"11,1",
+	"11,7",
+	"9,7",
+	"9,5",
+	"2,5",
+	"2,3",
+	"7,3",
+}
+
+func TestPartOne(t *testing.T) {
+	expected := 50
+	got := PartOne(testInput)
+	if got != expected {
+		t.Errorf("PartOne() = %d, want %d", got, expected)
+	}
+}