Verify existing multivalued attribute values using powershell

I am writing a powershell script which will add value to a multivalued reference attribute ( This multivalued reference attribute name is "Admins" and is binded to person object). 

Suppose I am adding value "Test"(Reference attribute) to multivalued reference attribute ("Admins").

I want to check whether the value  "Test" is already present in "Admins" before adding this value to multivalued reference attribute ("Admins"). Can someone please guide me on this.