Tests: Reduce RAM usage (#5577)

https://github.com/XTLS/Xray-core/pull/5577#issuecomment-3768963110

testing/scenarios/common.go

@@ -213,7 +213,8 @@ func testTCPConn2(conn net.Conn, payloadSize int, timeout time.Duration) func()
 				"\tSys =", units.ByteSize(m.Sys).String(),
 				"\tNumGC =", m.NumGC)
 		}()
-		payload := make([]byte, payloadSize)
+		singleWrite := func(length int) error {
+			payload := make([]byte, length)
 			common.Must2(rand.Read(payload))
 
 			nBytes, err := conn.Write(payload)
@@ -224,7 +225,7 @@ func testTCPConn2(conn net.Conn, payloadSize int, timeout time.Duration) func()
 				return errors.New("expect ", len(payload), " written, but actually ", nBytes)
 			}
 
-		response, err := readFrom2(conn, timeout, payloadSize)
+			response, err := readFrom2(conn, timeout, length)
 			if err != nil {
 				return err
 			}
@@ -236,6 +237,18 @@ func testTCPConn2(conn net.Conn, payloadSize int, timeout time.Duration) func()
 
 			return nil
 		}
+		for payloadSize > 0 {
+			sizeToWrite := 1024
+			if payloadSize < 1024 {
+				sizeToWrite = payloadSize
+			}
+			if err := singleWrite(sizeToWrite); err != nil {
+				return err
+			}
+			payloadSize -= sizeToWrite
+		}
+		return nil
+	}
 }
 
 func WaitConnAvailableWithTest(t *testing.T, testFunc func() error) bool {