diff --git a/internal/2025/DayThree/code_test.go b/internal/2025/DayThree/code_test.go
new file mode 100644
index 0000000..4e953fa
--- /dev/null
+++ b/internal/2025/DayThree/code_test.go
@@ -0,0 +1,18 @@
+package daythree
+
+import "testing"
+
+var testInput = []string{
+	"987654321111111",
+	"811111111111119",
+	"234234234234278",
+	"818181911112111",
+}
+
+func TestPartOne(t *testing.T) {
+	expected := 357
+	got := PartOne(testInput)
+	if got != expected {
+		t.Errorf("PartOne() = %d, want %d", got, expected)
+	}
+}