Testing golang middleware that modifies the request - testing

Question

I have some middleware that adds a context with a request id to a request.
func AddContextWithRequestID(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
var ctx context.Context
ctx = NewContextWithRequestID(ctx, r)
next.ServeHTTP(w, r.WithContext(ctx))
})}
How do I write a test for this ?

Answer 1

To test that, you need to run that handler passing in a request, and using a custom next handler that checks that the request was indeed modified.
You can create that handler as follows:
(I am assuming your NewContextWithRequestID adds a "reqId" key to the request with a "1234" value, you should of course modify the assertions as needed)
// create a handler to use as "next" which will verify the request
nextHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
val := r.Context().Value("reqId")
if val == nil {
t.Error("reqId not present")
}
valStr, ok := val.(string)
if !ok {
t.Error("not string")
}
if valStr != "1234" {
t.Error("wrong reqId")
}
})
You can then use that handler as your next one:
// create the handler to test, using our custom "next" handler
handlerToTest := AddContextWithRequestID(nextHandler)
And then invoke that handler:
// create a mock request to use
req := httptest.NewRequest("GET", "http://testing", nil)
// call the handler using a mock response recorder (we'll not use that anyway)
handlerToTest.ServeHTTP(httptest.NewRecorder(), req)
Putting everything together as a working test, that'd be the code below.
Note: I fixed a small bug in your original "AddContextWithRequestID", as the ctx value started with a nil value when you just declared it with no initialization.
import (
"net/http"
"context"
"testing"
"net/http/httptest"
)
func NewContextWithRequestID(ctx context.Context, r *http.Request) context.Context {
return context.WithValue(ctx, "reqId", "1234")
}
func AddContextWithRequestID(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
var ctx = context.Background()
ctx = NewContextWithRequestID(ctx, r)
next.ServeHTTP(w, r.WithContext(ctx))
})
}
func TestIt(t *testing.T) {
// create a handler to use as "next" which will verify the request
nextHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
val := r.Context().Value("reqId")
if val == nil {
t.Error("reqId not present")
}
valStr, ok := val.(string)
if !ok {
t.Error("not string")
}
if valStr != "1234" {
t.Error("wrong reqId")
}
})
// create the handler to test, using our custom "next" handler
handlerToTest := AddContextWithRequestID(nextHandler)
// create a mock request to use
req := httptest.NewRequest("GET", "http://testing", nil)
// call the handler using a mock response recorder (we'll not use that anyway)
handlerToTest.ServeHTTP(httptest.NewRecorder(), req)
}