How to validate thrown javascript exception using chai and mocha?

Question

I have MongoDB Query function which in which query params are validated Here is the function Note: user is mongoose model

function fetchData(uName)
{
    try{
        if(isParamValid(uName))
        {
            return user.find({"uName":uName}).exec()
        }
        else {
            throw "Invalid params"
        }
    }
    catch(e)
    {
        throw e
    }
}

To test this with invalid username values, I have written test code for that using mocha, chai, and chai-as-promised for promise-based functions

describe('Test function with invalid values', async ()=>{
    it('should catch exception', async () => {
        await expect(fetchData(inValidUserName)).to.throw()
    })

    it('should catch exception', async () => {
        await expect(fetchData(inValidUserName)).to.throw(Error)
    })

    it('should catch exception', async () => {
        await expect(fetchData(inValidUserName)).to.be.rejectedWith(Error)
    })

    it('should catch exception', async () => {
        await expect(fetchData(inValidUserName)).to.be.rejected
    })
})

None of them pass the test, How do I write a test case to handle exception for invalid userName values

score 1 · Accepted Answer · answered May 13 '20 at 12:38

1

You are passing the result of fetchData function call to expect function. Instead of calling the fetchData function inside expect function, pass a function to expect function.

it('should catch exception', async () => {
    await expect(() => fetchData(inValidUserName)).to.throw('Invalid params')
})

answered May 13 '20 at 12:38

Yousaf

27,861
6
44
69

Thanks for your answer, it works for me Do I need to change test code if I replace throw new Error("Invalid params") from throw "Invalid params" ?? – Krunal Sonparate May 13 '20 at 13:26
I don't think that you will need to change anything – Yousaf May 13 '20 at 13:31

score 0 · Answer 2 · answered May 13 '20 at 12:39

0

Use try/catch

it('should catch exception', async () => {
    try {
      await fetchData(inValidUserName);
    } catch(error) {
      expect(error).to.exist;
    }
})

answered May 13 '20 at 12:39

zishone

1,196
1
9
11

1

This solution will not work. Coz In this case, If fetchData function does not throw exception/error for invalidValues it will still pass the test case – Krunal Sonparate May 13 '20 at 13:29

How to validate thrown javascript exception using chai and mocha?

2 Answers2