Truffle测试因类型错误而失败

我有一个非常简单的合同,在Remix编辑器中工作得非常好。

我只想学松露。我发起了一个空松露项目,签订了合同,并成功地编译了它。

然而 truffle test 给出以下错误

合同:

pragma solidity ^0.4.18;


contract Greetings{

    string public message;

    constructor() public {
        message = "Hello";
    }

    function getGreeting() public view returns (string){
        return message;
    }

}

测试:

var Greetings = artifacts.require("Greetings");


contract('Greetings Test', async (accounts) => {
    it("check for greetings message", async () => {
        let greeting = await Greetings.deployed();
        let message = await greeting.getGreeting().call();         
        console.log(message);
    });
});

错误:

 Contract: Greetings Test
    1) check for greetings message
    > No events were emitted


  0 passing (103ms)
  1 failing

  1) Contract: Greetings Test
       check for greetings message:
     TypeError: greeting.getGreeting(...).call is not a function
      at Context.it (test/campaignfactory.js:7:52)
      at <anonymous>
      at process._tickCallback (internal/process/next_tick.js:188:7)

注:我想用 asnyc/await .