$ go get github.com/asticode/go-gozzle/gozzle

import (
    "github.com/asticode/go-gozzle/gozzle"
)

// Create gozzle
g := gozzle.NewGozzle()

// Create a request set
reqSet := gozzle.NewRequestSet()

// Create the first request
r := NewRequest("my-first-request", gozzle.MethodGet, "/my-first-endpoint")

// Add headers
r.AddHeader("X-MyHeader", "MyValue")

// Add query
r.SetQuery(map[string]string{
    "api_key": "my_api_key",
    "access_token": "my_access_token",
})

// Set the callback that is executed before sending the request
r.SetBeforeHandler(func(r gozzle.Request) bool {
    if r.GetHeader("X-MyHeader") != "MyValue" {
        // Request will be sent
        return true
    } else {
        // Request will not be sent
        return false
    }
})

// Add the request to the request set
reqSet.AddRequest(r)

// Create the second request
r = NewRequest("my-second-request", gozzle.MethodPost, "/my-second-endpoint")

// Add a body to the request
r.SetBody(map[string]interface{}{
    "name": "Asticode",
    "email": "test@asticode.com",
})

// Set the callback that is executed after sending the request
r.SetAfterHandler(func(req gozzle.Request, resp gozzle.Response) {
    b, e := ioutil.ReadAll(resp.BodyReader())
    fmt.Println(fmt.Sprintf("Body %s for path %s", string(b), req.Path())
})

// Add the request to the request set
reqSet.AddRequest(r)

// Execute the 2 requests asynchronously
respSet := g.Exec(reqSet)

// Make sure the responses are properly closed
defer respSet.Close()

// Process responses
// The first request has not been sent because of the beforeHandler so only one response should be stored
for _, name := range respSet.Names() {
    req := reqSet.GetRequest(name)
    resp := respSet.GetResponse(name)
    if len(resp.Errors()) > 0 {
        fmt.Println(fmt.Sprintf("Error in request to %s", req.Path()))
    } else {
        fmt.Println(fmt.Sprintf("Request to %s was successful", req.Path()))
    }
}