This test has many dimensions to it. It has little to do with the guilt or innocence of the woman.
In order for the test to apply, the woman must become foolish. This has been interpreted to mean that she has aroused her husband's jealousy by flirting. Or she has aroused the suspicion of witnesses to her flirting, but they have not witnessed adultery, and have made it known to the husband.
The time of causing suspicion must be followed by a period of sufficient length of time where the two were isolated together and had opportunity for adultery. see Rashi's comments
If the husband is suspicious, the test is a method of being reconciled.
If the community is suspicious, the husband may not have relations with her until she is cleared.
The first effect of the law is that it is a deterrent. And apparently an effective one since part of the law is that a woman so condemned would become a curse. Her name would be used in a phrase such as '...may you be as so-and-so who cheated on her husband." There is no record of a woman who has become such a curse.
The second effect is that innocent women are not put away because of libelous suspicions of the community or simple jealousies of the husband.
The third effect is that it caused a jealous husband to reconsider his jealousy. If she had really been unfaithful, she would die during the test. He had to consider if he really wanted to put her to death, or to grant mercy in the absence of proof.
The OP asks why is there not a test for the suspected man. The simple answer is that a woman could not divorce her husband even if he was unfaithful, nor could she have him put to death.
1Co 11:8 For the man is not of the woman; but the woman of the man.
1Co 11:9 Neither was the man created for the woman; but the woman for
However, some have interpreted that the test also applies to the adulterer:
causing the belly to swell and the thigh to rupture: [This refers to]
the belly and thigh of the adulterer, or perhaps only those of the
adulteress? [However,] when Scripture says “causes your thigh to
rupture and your belly to swell” (verse 21), those of the adulteress
are stated [thus here it must refer to the adulterer]. — [Sotah 28a
and Sifrei Naso 1:65]
If the man and the woman were guilty, they could either confess and be stoned, or face the test, hoping to gain mercy from God, which would certainly be a life-changing event.
Addendum: Christian symbolism of this passage
The man is Christ and the wife is the church. The church is a prostitute that has been made into a virgin. Christ's jealousy is appeased through the realities of the symbolic offerings.
Water is the word of God which brings life or death. And such is the bitter water that the woman must drink.
The grain offering is a similitude of the seed of the woman, Christ himself. The wave offering is symbolic of Christ being offered on the cross, but being kept on earth within the body of Christ. He goes but stays. The burnt portion is a remembrance of Christ's total devotion to the FAther and his bride.
The oath the woman took is the devotion to Christ in her trust that only He can give her mercy, though she be guilty or innocent. She trusts Him to be the righteous and merciful judge.
The curses against the church are written in a book but blotted out with the living water of Christ. The salvation gained through Christ comes with the bitterness of the cross.
Those who are accepted by Christ have been made clean by his blood. Christ is guiltless in the condemnation of the wicked.