Tex. Estates Code § 256.153

(a) An attested will produced in court that is not self-proved as provided by this title may be proved in the manner provided by this section.

(b) A will described by Subsection (a) may be proved by the sworn testimony or affidavit of one or more of the subscribing witnesses to the will taken in open court.

(c) If all the witnesses to a will described by Subsection (a) are nonresidents of the county or the witnesses who are residents of the county are unable to attend court, the will may be proved:

(1) by the sworn testimony of one or more of the witnesses by written or oral deposition taken in accordance with Section 51.203 or the Texas Rules of Civil Procedure;

(2) if no opposition in writing to the will is filed on or before the date set for the hearing on the will, by the sworn testimony or affidavit of two witnesses taken in open court, or by deposition as provided by Subdivision (1), to the signature or the handwriting evidenced by the signature of:

(A) one or more of the attesting witnesses; or

(B) the testator, if the testator signed the will; or

(3) if it is shown under oath to the court's satisfaction that, after a diligent search was made, only one witness can be found who can make the required proof, by the sworn testimony or affidavit of that witness taken in open court, or by deposition as provided by Subdivision (1), to a signature, or the handwriting evidenced by a signature, described by Subdivision (2).

(d) If none of the witnesses to a will described by Subsection (a) are living, or if each of the witnesses is a member of the armed forces or the armed forces reserves of the United States, an auxiliary of the armed forces or armed forces reserves, or the United States Maritime Service and is beyond the court's jurisdiction, the will may be proved:

(1) by two witnesses to the handwriting of one or both of the subscribing witnesses to the will or the testator, if the testator signed the will, by:

(A) sworn testimony or affidavit taken in open court; or

(B) written or oral deposition taken in accordance with Section 51.203 or the Texas Rules of Civil Procedure; or

(2) if it is shown under oath to the court's satisfaction that, after a diligent search was made, only one witness can be found who can make the required proof, by the sworn testimony or affidavit of that witness taken in open court, or by deposition as provided by Subdivision (1), to a signature or the handwriting described by Subdivision (1).

(e) A witness being deposed for purposes of proving the will as provided by Subsection (c) or (d) may testify by referring to a certified copy of the will, without the judge requiring the original will to be removed from the court's file and shown to the witness.