test: add an almost arbitrary test for p2

internal/2015/DaySeven/code_test.go

@@ -23,3 +23,28 @@ func TestPartOne(t *testing.T) {
 		t.Errorf("PartOne() = %d, want %d", got, expected)
 	}
 }
+
+func TestPartTwo(t *testing.T) {
+	instructions := map[string]string{
+		"x": "10",
+		"y": "20",
+		"z": "x AND y",
+		"b": "z",
+		"w": "b LSHIFT 1",
+		"v": "NOT b",
+		"u": "w OR v",
+		"a": "u",
+	}
+
+	partOneResult := PartOne(instructions)
+	bValue := uint16(partOneResult)
+	w := bValue << 1
+	v := ^bValue
+	u := w | v
+	expected := int(u)
+
+	got := PartTwo(instructions)
+	if got != expected {
+		t.Errorf("PartTwo() = %d, want %d (PartOne result: %d)", got, expected, partOneResult)
+	}
+}