Improve client/server tests

Tests must not call *testing.T methods after the test function returns.
Use a sync.WaitGroup to ensure that server handler functions complete
before tests return.

client_server_test.go

@@ -23,6 +23,7 @@ import (
 	"net/url"
 	"reflect"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 )
@@ -44,12 +45,15 @@ var cstDialer = Dialer{
 	HandshakeTimeout: 30 * time.Second,
 }
 
-type cstHandler struct{ *testing.T }
+type cstHandler struct {
+	*testing.T
+	s *cstServer
+}
 
 type cstServer struct {
-	*httptest.Server
-	URL string
-	t   *testing.T
+	URL    string
+	Server *httptest.Server
+	wg     sync.WaitGroup
 }
 
 const (
@@ -58,9 +62,15 @@ const (
 	cstRequestURI = cstPath + "?" + cstRawQuery
 )
 
+func (s *cstServer) Close() {
+	s.Server.Close()
+	// Wait for handler functions to complete.
+	s.wg.Wait()
+}
+
 func newServer(t *testing.T) *cstServer {
 	var s cstServer
-	s.Server = httptest.NewServer(cstHandler{t})
+	s.Server = httptest.NewServer(cstHandler{T: t, s: &s})
 	s.Server.URL += cstRequestURI
 	s.URL = makeWsProto(s.Server.URL)
 	return &s
@@ -68,13 +78,19 @@ func newServer(t *testing.T) *cstServer {
 
 func newTLSServer(t *testing.T) *cstServer {
 	var s cstServer
-	s.Server = httptest.NewTLSServer(cstHandler{t})
+	s.Server = httptest.NewTLSServer(cstHandler{T: t, s: &s})
 	s.Server.URL += cstRequestURI
 	s.URL = makeWsProto(s.Server.URL)
 	return &s
 }
 
 func (t cstHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// Because tests wait for a response from a server, we are guaranteed that
+	// the wait group count is incremented before the test waits on the group
+	// in the call to (*cstServer).Close().
+	t.s.wg.Add(1)
+	defer t.s.wg.Done()
+
 	if r.URL.Path != cstPath {
 		t.Logf("path=%v, want %v", r.URL.Path, cstPath)
 		http.Error(w, "bad path", http.StatusBadRequest)