All 3 Uses

Old Testament
in
To Kill a Mockingbird
(Edited)

Miss Maudie's face likened such an occurrence unto an Old Testament pestilence.
p. 47.8

Old Testament = from the sacred scripture of the Hebrews which is the first half of the Christian Bible
...for all he knows we mighta come straight out of Ethiopia durin' the Old Testament.
p. 184.3 *

Old Testament = the sacred scripture of the Hebrews which is the first half of the Christian Bible
Well if we came out durin' the Old Testament it's too long ago to matter.
p. 184.4

Definitions:

(1) (Old Testament)
the collection of books comprising the sacred scripture of the Hebrews (Jews) which is the first half of the Christian Bible

In academic circles, the term Hebrew Bible is commonly used to refer to the Old Testament. Most scholars agree that it was written and compiled between the 12th and the 2nd century BC.
(2) (meaning too rare to warrant focus)