/scoreboard is lock on certain domain

• I created a new scoreborad about a health (/scoreboard objectives add test health)
• I inserted this command : " /scoreboard players set @s test " and he asks me : "Unknown order".
• I must to insert " /scoreboard players set @s test 0" and I did this.
• He say me "I must take of "0"" .... I don't understand.