How can I test HTTPS endpoints in go?

So I'm trying to mock out a response to an https request using httptest.TLSServer but the http.Client making the request keeps telling me that the server is giving an invalid http response. I bet this is because there's no actual SSL cert. Is there any way I can get the client to ignore tls while still mocking out an https request?

The test code in question

func TestFacebookLogin(t *testing.T) {
    db := glob.db
    server := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        resp := `
        {
          "id": "123",
          "email": "blah",
          "first_name": "Ben",
          "last_name": "Botwin"
        }
        `

        w.Write([]byte(resp))
    }))
    defer server.Close()

    transport := &http.Transport{
        Proxy: func(r *http.Request) (*url.URL, error) {
            return url.Parse(server.URL)
        },
    }

    svc := userService{db: db, client: &http.Client{Transport: transport}}

    _, err := svc.FacebookLogin("asdf")

    if err != nil {
        t.Errorf("Error found: %s", err)
    }

}

And the request that I'm trying to make:

url := "https://<Some facebook api endpoint>"
req, err := http.NewRequest("GET", url, nil)
resp, err := client.Do(req)
if err != nil {
    return nil, err
}
defer resp.Body.Close()