Mass. Gen. Laws ch. 233 § 20
Any person of sufficient understanding, although a party, may testify in any proceeding, civil or criminal, in court or before a person who has authority to receive evidence, except as follows:
First, Except in a proceeding arising out of or involving a contract made by a married woman with her husband, a proceeding under chapter two hundred and nine D and in a prosecution begun under sections one to ten, inclusive, of chapter two hundred and seventy-three, any criminal proceeding in which one spouse is a defendant alleged to have committed a crime against the other spouse or to have violated a temporary or permanent vacate, restraining, or no-contact order or judgment issued pursuant to section eighteen, thirty-four B or thirty-four C of chapter two hundred and eight, section thirty-two of chapter two hundred and nine, section three, three B, three C, four, or five of chapter two hundred and nine A, or sections fifteen or twenty of chapter two hundred and nine C, or a similar protection order issued by another jurisdiction, obtained by the other spouse, and except in a proceeding involving abuse of a person under the age of eighteen, including incest, neither husband nor wife shall testify as to private conversations with the other.
Second, Except as otherwise provided in section seven of chapter two hundred and seventy-three and except in any proceeding relating to child abuse, including incest, neither husband nor wife shall be compelled to testify in the trial of an indictment, complaint or other criminal proceeding against the other;
Third, The defendant in the trial of an indictment, complaint or other criminal proceeding shall, at his own request, but not otherwise, be allowed to testify; but his neglect or refusal to testify shall not create any presumption against him.
Fourth, A parent shall not testify against the parent's minor child and a minor child shall not testify against the child's parent in a proceeding before an inquest, grand jury, trial of an indictment or complaint or any other criminal, delinquency or youthful offender proceeding in which the victim in the proceeding is not a family member and does not reside in the family household; provided, however, that for the purposes of this clause, "parent" shall mean the biological or adoptive parent, stepparent, legal guardian or other person who has the right to act in loco parentis for the child; provided further, that in a case in which the victim is a family member and resides in the family household, the parent shall not testify as to any communication with the minor child that was for the purpose of seeking advice regarding the child's legal rights.
Mass. Gen. Laws ch. 233, § 20