What is attorney-client privilege and what is the test?

The attorney-client privilege is a privilege to refuse to disclose, and to prevent another from disclosing, a confidential communication between client and lawyer.... (Evid. Code, 954.) A client within the meaning of the attorney-client privilege is a person who, directly or through an authorized representative, consults a lawyer for the purpose of retaining the lawyer or securing legal services or advice [from the lawyer in the lawyer's] professional capacity. (Evid. Code, 951.) A confidential communication between client and lawyer means information transmitted between a client and his or her lawyer in the course of [the attorney-client] relationship and in confidence by a means which, so far as the client is aware, discloses the information to no third persons other than those present to further the [client's] interest ... in the consultation or those to whom disclosure is reasonably necessary for transmission of the information or the accomplishment of the purpose for which the attorney is consulted. (Evid. Code, 952.) [T]he privilege applies not only to communications made in anticipation of litigation, but also to legal advice when no litigation is threatened. (Roberts v. City of Palmdale(1993) 5 Cal.4th 363, 371, 20 Cal.Rptr.2d 330, 853 P.2d 496.)