(a) Admissions. Upon the trial of the action, the court may admit proof of the admissions of the parties to be received in evidence, excluding such as shall appear to have been obtained by connivance, fraud, coercion, or other improper means.
(b) Marriage. Testimony admissible to prove a common-law marriage may be received as evidence of the marriage of the parties.
(c) Husband and wife as witness. Either party to the action shall be competent to testify upon all material matters involved in the controversy.
(d) Corroborating testimony. A decree of divorce, separate maintenance or annulment may be granted upon the uncorroborated testimony of either party or both of them.