test: add unit test for part one

internal/2025/DayFive/code_test.go

@@ -0,0 +1,25 @@
+package dayfive
+
+import "testing"
+
+var testInput = []string{
+	"3-5",
+	"10-14",
+	"16-20",
+	"12-18",
+	"",
+	"1",
+	"5",
+	"8",
+	"11",
+	"17",
+	"32",
+}
+
+func TestPartOne(t *testing.T) {
+	expected := 3
+	got := PartOne(testInput)
+	if got != expected {
+		t.Errorf("PartOne() = %d, want %d", got, expected)
+	}
+}