Before discussing an uncontested versus a contested divorce you must also understand  that there are two types of divorce in Virginia.  The first is a divorce a mensa et thoro, which means a divorce from board and bed, which is really a legal separation and not a final decree.  The second is a divorce a vinculo matrimonii, or a divorce from the bond of matrimony which is an absolute divorce.  The pertinent code sections are §§ 20-91 and 20-95.

 § 20-91. Grounds for divorce from bond of matrimony; contents of decree.
    A. A divorce from the bond of matrimony may be decreed:
(1) For adultery; or for sodomy or buggery committed outside the marriage;
(2) [Repealed.]
(3) Where either of the parties subsequent to the marriage has been convicted of a felony, sentenced to confinement for more than one year and confined for such felony subsequent to such conviction, and cohabitation has not been resumed after knowledge of such confinement (in which case no pardon granted to the party so sentenced shall restore such party to his or her conjugal rights);
 (4), (5) [Repealed.]
  (6) Where either party has been guilty of cruelty, caused reasonable apprehension of bodily hurt, or willfully deserted or abandoned the other, such divorce may be decreed to the innocent party after a period of one year from the date of such act; or
 (7), (8) [Repealed.]
(9)(a) On the application of either party if and when the husband and wife have lived separate and apart without any cohabitation and without interruption for one year. In any case where the parties have entered into a separation agreement and there are no minor children either born of the parties, born of either party and adopted by the other or adopted by both parties, a divorce may be decreed on application if and when the husband and wife have lived separately and apart without cohabitation and without interruption for six months. A plea of res adjudicata or of recrimination with respect to any other provision of this section shall not be a bar to either party obtaining a divorce on this ground; nor shall it be a bar that either party has been adjudged insane, either before or after such separation has commenced, but at the expiration of one year or six months, whichever is applicable, from the commencement of such separation, the grounds for divorce shall be deemed to be complete, and the committee of the insane defendant, if there be one, shall be made a party to the cause, or if there be no committee, then the court shall appoint a guardian ad litem to represent the insane defendant.
 (b) This subdivision (9) shall apply whether the separation commenced prior to its enactment or shall commence thereafter. Where otherwise valid, any decree of divorce hereinbefore entered by any court having equity jurisdiction pursuant to this subdivision (9), not appealed to the Supreme Court of Virginia, is hereby declared valid according to the terms of said decree notwithstanding the insanity of a party thereto.
 (c) A decree of divorce granted pursuant to this subdivision (9) shall in no way lessen any obligation any party may otherwise have to support the spouse unless such party shall prove that there exists in the favor of such party some other ground of divorce under this section or § 20-95

§ 20-95. Grounds for divorces from bed and board. — A divorce from bed and board may be decreed for cruelty, reasonable apprehension of bodily hurt, willful desertion or abandonment.

 Since Virginia is a no-fault divorce state, which really means the only grounds for a divorce is that one person wants it, there is not much a person can do to prevent their spouse from obtaining the divorce.  Paragraph 9(a) of § 20-91 gives the conditions that must be met.  However, there are a few defenses for a divorce on other grounds, specifically adultery.
 The first is condoning or forgiveness. When the suit is for divorce for adultery, sodomy, or buggery, the divorce shall not be granted, if it appear that the parties voluntarily cohabited after the knowledge of the fact of adultery, sodomy or buggery, or that it occurred more than five years before the institution of the suit (Virginia Code § 20-94).  The second is that it was committed by the procurement or connivance of the party alleging such act (Virginia Code § 20-94).   In other words the party suing for adultery arranged the act by asking or paying someone to commit the act with their spouse.  The final defense is that the parties are not legally married since the marriage was a sham or is voidable.  Of course this defense is a two edged sword—you can’t be divorced since you are not married! 
However, such a defense is no good if the couple held themselves out to the public as man and wife for two years or more.  Of note, this situation is what defines a common law marriage in many states.  Virginia will recognize a common law marriage from another state for purposes of a divorce proceeding initiated in the Commonwealth.  However, Virginia will not recognize cohabitation in Virginia as constituting a marriage. You must be married in Virginia under the requirements of the code for the marriage to be valid in the Commonwealth.  Also, Virginia recognizes a same sex marriage only for the purpose of property distribution and child custody/visitation/support issues.  A same sex union must be terminated in the state of the marriage before Virginia can act on any residual divorce actions such as property or children.
An uncontested divorce can be obtained if the parties are in agreement on all the issues required to terminate the marriage.  The requirements are listed in § 20-91(A)(9)(a) of the Virginia Code and listed above.  In summary, if there are no minor children either born of the parties, born of either party and adopted by the other or adopted by both parties, and the parties have lived separate and apart for six months, then they may divorce.  Otherwise they must not cohabitate for one year to obtain the divorce.
If they are in disagreement on any statutory issue and it must be litigated, then the divorce is contested.  This is significant only in the fees paid for the divorce.  An uncontested divorce obtained through our services can be obtained for far less than $1,000.  Our fee for the divorce is $450, and there are court costs and process server fees (generally an additional $84 and $24 respectively).  Also a Separation and Stipulation agreement will cost $250.  A contested divorce requires a $2,500 retainer to be paid up front to start the divorce and the final decree may cost you $8,000 or more, depending on how much the parties cannot resolve the differences on their own.