Heck Tate's courtroom testimony occurs in Chapter 17 of the novel. After the prosecutor has finished questioning Sheriff Tate, Atticus asks Heck Tate several times if a doctor was called to the Ewell house after the "attack" on Mayella Ewell.
More significantly, when Tate begins describing Mayella's injuries, Atticus asks him repeatedly which side of the face Mayella's injuries were on. When the sheriff replies that the injuries were on Mayella's left side, Atticus asks him to clarify if that is his left side or the actual right side of a person standing across from him. The sheriff realizes his error and says that it was Mayella's right eye. Atticus wants the court record to be accurate because the fact is pertinent to his defense of Tom Robinson, so he asks the court reporter to read back what Sheriff Tate said. The court reporter reads,
" 'Mr. Finch. I remember now she was bunged up on that side of the face' " (225).
Atticus's persistence gets Heck Tate to testify clearly that Mayella's right side was the bruised side. If you have not read past Chapter 17 in the novel, I do not want to give anything away. But consider Heck Tate's testimony when you read the chapters featuring Atticus's questioning of Bob Ewell and Tom Robinson.