In a large wok, heat 2 teaspoons oil over high. Add the long beans and cook, tossing occasionally, until blistered, about 3 minutes. Add the remaining 4 teaspoons oil along with the mushrooms and bok choy leaves, season with salt, and cook, stirring, until the bok choy has wilted, about 3 more minutes. Add the shrimp and cook, tossing, until just cooked through, about 4 minutes. Stir in the XO sauce, remove the wok from the heat, and transfer the beans to a platter before serving.