Using custom URL for httptest.NewServer in Go - unit-testing

Question

I am running UT on some rest calls by creating a http test server in the Go language. My code is as follows.
type student struct{
FirstName string
LastName string
}
func testGetStudentName() {
testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
response = new(student)
response.FirstName = "Some"
response.LastName = "Name"
b, err := json.Marshal(response)
if err == nil {
fmt.Fprintln(w, string(b[:]))
}
}))
defer ts.Close()
student1 := base.getStudent("123")
log.Print("testServerUrl",testServer.URL) //prints out http://127.0.0.1:49931 ( port changes every time this is run)
ts.URL = "http://127.0.0.1:8099" //this assignment does not quite change the URL of the created test server.
}
In the file being tested,
var baseURL = "http://originalUrl.com"
var mockUrl = "http://127.0.0.1:49855"
func Init(mockServer bool){
if mockServer {
baseURL = mockUrl
}
}
func getStudent(id String){
url := baseUrl + "/student/" + id
req, err := http.NewRequest("GET", url, nil)
}
This init is called from my test.
This creates a new test server and runs the calls on a random port. Is it possible for me to run this server on a port I specify?

Answer 1

Most applications use the port assigned in NewServer or NewUnstartedServer because this port will not conflict with a port in use on the machine. Instead of assigning a port, they set the base URL for the service to the test server's URL.
If you do want to set the listening port, do the following:
// create a listener with the desired port.
l, err := net.Listen("tcp", "127.0.0.1:8080")
if err != nil {
log.Fatal(err)
}
ts := httptest.NewUnstartedServer(handler)
// NewUnstartedServer creates a listener. Close that listener and replace
// with the one we created.
ts.Listener.Close()
ts.Listener = l
// Start the server.
ts.Start()
// Stop the server on return from the function.
defer ts.Close()
// Add your test code here.