Legal basis: code of conduct for lawyers.
Article 62 A lawyer shall investigate and collect evidence according to law.
Article 63 A lawyer shall not submit evidence that he knows to be false to a judicial organ or an arbitration institution.
Article 64 A lawyer who testifies in court will no longer be entrusted as a defender or agent in this case.
Article 35 of the Lawyers Law of People's Republic of China (PRC) * * * An entrusted lawyer may, according to the needs of the case, apply to the people's procuratorate or the people's court for collecting and obtaining evidence or to the people's court for notifying witnesses to testify in court. If a lawyer investigates and collects evidence by himself, he may, with the lawyer's practice certificate and the certificate of the law firm, investigate the situation related to undertaking legal affairs with the relevant units or individuals.