rpcsrv: fix TestWSClientsLimit

Made connections in parallel to check the limit and attempt to make one
more connection beyond the limit. Only "default" test case is failing,
because default number of connections is 64 (quite large for slow
runners). The failure reason is:
* given ~1 second for [dealing + request] per connection (time is taken
from the test log)
* by the moment 65-th connection is reached, some connections from the
start of the test have died due to inactivity (this process literally
takes 1 minute)

Signed-off-by: Ekaterina Pavlova <ekt@morphbits.io>

pkg/services/rpcsrv/subscription_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -604,25 +605,37 @@ func TestWSClientsLimit(t *testing.T) {
 			dialer := websocket.Dialer{HandshakeTimeout: 5 * time.Second}
 			url := "ws" + strings.TrimPrefix(httpSrv.URL, "http") + "/ws"
 			wss := make([]*websocket.Conn, effectiveClients)
+			var wg sync.WaitGroup
 
-			for i := 0; i < len(wss)+1; i++ {
+			// Dial effectiveClients connections in parallel
+			for i := 0; i < effectiveClients; i++ {
+				wg.Add(1)
+				j := i
+				go func() {
+					defer wg.Done()
 					ws, r, err := dialer.Dial(url, nil)
-				if r != nil && r.Body != nil {
+					if r != nil {
 						defer r.Body.Close()
 					}
-				if i < effectiveClients {
 					require.NoError(t, err)
-					wss[i] = ws
-					// Check that it's completely ready.
+					wss[j] = ws
 					doSomeWSRequest(t, ws)
-				} else {
-					require.Error(t, err)
+				}()
 			}
+
+			wg.Wait()
+
+			// Attempt one more connection, which should fail
+			_, r, err := dialer.Dial(url, nil)
+			require.Error(t, err, "The connection beyond the limit should fail")
+			if r != nil {
+				r.Body.Close()
 			}
 			// Check connections are still alive (it actually is necessary to add
 			// some use of wss to keep connections alive).
-			for i := 0; i < len(wss); i++ {
-				doSomeWSRequest(t, wss[i])
+			for _, ws := range wss {
+				doSomeWSRequest(t, ws)
+				ws.Close()
 			}
 		})
 	}