test: add unit test for part one

internal/2017/DayTwo/code_test.go

@@ -0,0 +1,17 @@
+package daytwo
+
+import "testing"
+
+var testInput = [][]int{
+	{5, 1, 9, 5},
+	{7, 5, 3},
+	{2, 4, 6, 8},
+}
+
+func TestPartOne(t *testing.T) {
+	got := PartOne(testInput)
+	expected := 18
+	if got != expected {
+		t.Errorf("PartOne() = %d, want %d", got, expected)
+	}
+}