Golang How to stub a method inside another?

I've asked this before and that never got anywhere other than getting a generic response saying have a look at things like stdlib, so here I'm taking a crack at testing in Go again.

I'm writing a web app that will send requests to another third-party service do some calculations and send it back to the fronted.

Here are the relevant parts for the test I'm trying to writer.

client.go

func (c *ClientResponse) GetBankAccounts() (*BankAccounts, *RequestError) {
    req, _ := http.NewRequest("GET", app.BuildUrl("bank_accounts"), nil)
    params := req.URL.Query()
    params.Add("view", "standard_bank_accounts")
    req.URL.RawQuery = params.Encode()

    c.ClientDo(req)
    if c.Err.Errors != nil {
        return nil, c.Err
    }

    bankAccounts := new(BankAccounts)
    defer c.Response.Body.Close()
    if err := json.NewDecoder(c.Response.Body).Decode(bankAccounts); err != nil {
        return nil, &RequestError{Errors: &Errors{Error{Message: "failed to decode Bank Account response body"}}}
    }

    return bankAccounts, nil
}

helper.go

type ClientResponse struct {
    Response *http.Response
    Err      *RequestError
}

type ClientI interface {
    ClintDo(req *http.Request) (*http.Response, *RequestError)
}

func (c *ClientResponse) ClientDo(req *http.Request) {
    //Do some authentication with third-party service

    errResp := *new(RequestError)
    client := http.Client{}
    resp, err := client.Do(req)
    if err != nil {
        // Here I'm repourposing the third-party service's error response mapping
        errResp.Errors.Error.Message = "internal server error. failed create client.Do"
    }
    c.Response = resp
    c.Err = &errResp
}

My problem currently is I only want to test the GetBankAccounts() method so I want to stub the ClientDo, but I'm at a lost on how to do that. Here's what I have so far with my test case.

client_test.go

type StubClientI interface {
    ClintDo(req *http.Request) (*http.Response, *RequestError)
}

type StubClientResponse struct {}

func (c *StubClientResponse) ClientDo(req *http.Request) (*http.Response, *RequestError) {
    return nil, nil
}

func TestGetBankAccounts(t *testing.T) {
    cr := new(ClientResponse)
    accounts, err := cr.GetBankAccounts()
    if err != nil {
        t.Fatal(err.Errors)
    }
    t.Log(accounts)
}

The ClintDo still pointing to the actual method on the helper.go, how can I make it use the on in the test?

Any help on this would be much appreciated, as this started to drive me up the walls, to say an understatement.

Thanks in advance.