How to mock a function returned by a mocked function

Question

I am trying to write mock a test for the following function call

const contract = await new web3.eth.Contract();

tx.data = await contract.methods
  .setup(
    [juryAddress, buyerAddress, sellerAddress],
    threshold,
    to,
    txData,
    fallbackHandler,
    paymentToken,
    0,
    sellerAddress
  )
  .encodeABI();

I am trying to mock this as a function contract.methods.setup() that returns a function object encodeABI() which then returns a dummy value {}.

The mock I am trying looks like this, although it is not working

const encodeABI = jest.fn()
encodeABI.mockReturnValue({})

const contract = {
    methods: {
        setup: jest.fn(),
    }
}

eth.Contract.mockResolvedValue(contract)
contract.methods.setup.mockResolvedValue(encodeABI)
expect(encodeABI).toBeCalled()

expect(encodeABI).toBeCalled() is not being called as I expect

mockResolvedValue() returns a Promise. Are you sure you don't just want contract.methods.setup.mockReturnValue(encodeABI) instead? — Phil
– Phil, Commented Jun 1, 2021 at 23:25
@Phil I thought I would want to return a promise for setup(), since contract.methods.setup() is async, right? — Jack DiSalvatore
– Jack DiSalvatore, Commented Jun 1, 2021 at 23:40
It doesn't appear to be. Your code just calls contract.methods.setup(...).encodeABI(). If anything, it's encodeABI() that should return a Promise since that's what you are awaiting — Phil
– Phil, Commented Jun 1, 2021 at 23:45
thanks, you are right, I think I have it backwards then. contract.methods.setup() returns a value, and .encodeABI() returns the Promise. — Jack DiSalvatore
– Jack DiSalvatore, Commented Jun 1, 2021 at 23:48

Phil · Accepted Answer · 2021-06-01 23:54:42Z

1

Your production code awaits encodeABI(), not setup(). It expects setup() to return an object with an encodeABI() function, not a Promise.

I would recommend making the following changes

const encodeABI = jest.fn(async () => ({})) // return a Promise here

const contract = {
    methods: {
        setup: jest.fn(() => ({ encodeABI })) // return an object with encodeABI
    }
}

edited Jun 1, 2021 at 23:54

answered Jun 1, 2021 at 23:47

Phil

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