How to unit test the http.ServeFile [duplicate]

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• How to test http request handlers 1 answer

There is the most common controller that returns files, there is a need to conduct unit testing, but there’s no idea how to do it. In the tests i'm receiving 404 error, cause file not found in FS, maybe there a way to mock the fs.Open() calls in the http module?

func GetProfileAvatarHandler() http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {

        if r.Header.Get("something") == "there" {
            http.ServeFile(w, r, "images/default_avatar.jpg")
            return
        }

        http.ServeFile(w, r, "images/user_avatar.jpg")
    }
}