The people who testify at Tom Robinson’s trial are Sherriff Tate, Bob Ewell, Mayella Ewell, and Tom Robinson.
Heck Tate is the first to testify in chapter 17. He describes how he has called in when Mayella was injured, and how she accused Tom of raping her.
"Found her lying on the floor in the middle of the front room, one on the right as you go in. She was pretty well beat up …. I asked her who hurt her and she said it was Tom Robinson-" (ch 17)
Although Heck Tate is a good man and a friend of Atticus, he is doing his job. As the first responder, he needed to tell the jury what he saw. He relays the facts somewhat colorfully, but basically sticks to the facts. He treats both Mr. Gilmer and Atticus civilly.
Next, Bob Ewell is called. He is Mayella’s father, and his full name is Robert E. Lee Ewell. Mr. Ewell seems to enjoy the attention, and is rough, coarse, and rude. He is even rude to Mr. Gilmer, who is supposed to be on his side.
"Are you the father of Mayella Ewell?" was the next question. "Well, if I ain't I can't do nothing about it now, her ma's dead," was the answer. (ch 17)
This answer gets the courtroom stirred up and annoys Judge Taylor, who tells him to behave. Mr. Ewell is not very smart, and has a hard time understanding some of the questions.
Next Bob Ewell’s daughter Mayella is called. She is the victim. She is young, and very intimidated by the entire process. She thinks Atticus is making fun of her when he tries to be polite. Mr. Gilmer even objects, saying that Atticus is browbeating the witness.
Judge Taylor laughed outright. "Oh sit down, Horace, he's doing nothing of the sort. If anything, the witness's browbeating Atticus." (ch 18)
Scout was feeling sorry for Mayella. Atticus had her carefully describe her life, and Scout realizes she is very lonely. She is beginning to show empathy.
When Tom Robinson takes the stand, he demonstrates that he is crippled. The lack of use of one of his arms is very important to Atticus’s case, and he has carefully built up to it by establishing where Mayella’s injuries are.
Atticus was trying to show …. that Mr. Ewell could have beaten up Mayella.…. If her right eye was blacked and she was beaten mostly on the right side of the face, it would tend to show that a left-handed person did it. (ch 17)
In fact, since Tom Robinson cannot use his left hand because of an accident, he seems to be in the clear. Unfortunately, he makes the mistake of saying he feels sorry for Mayella. The jury does not like it when a black man feels sorry for a white woman.
All in all, it is a pretty short trial with not much testimony. Atticus makes a good case, but he can't overcome the racism that pervades Maycomb.