Test case: spell kills give XP

TEST_CASE("Kills with spells give XP") {
  GIVEN("a high-damage spell and low-health NPC") {
    auto data = R"(
      <spell id="nuke" range=30 >
        <targets enemy=1 />
        <function name="doDirectDamage" i1=99999 />
      </spell>
      <npcType id="critter" maxHealth=1 />
    )";
    auto s = TestServer::WithDataString(data);
    s.addNPC("critter", {10, 15});

    WHEN("a user knows the spell") {
      auto c = TestClient::WithDataString(data);
      s.waitForUsers(1);
      auto &user = s.getFirstUser();
      user.getClass().teachSpell("nuke");

      AND_WHEN("he kills the NPC with the spell") {
        const auto &critter = s.getFirstNPC();
        c.sendMessage(CL_SELECT_ENTITY, makeArgs(critter.serial()));
        c.sendMessage(CL_CAST, "nuke");
        WAIT_UNTIL(critter.isDead());

        THEN("the user has some XP") { CHECK(user.xp() > 0); }
      }
    }
  }
}