Disable calling read on the output expressions and definitions, which can be useful when the output contain unbalanced parenthesis, or do not otherwise match the language’s syntax, for example:

#lang repltest racket
> (displayln "(unbalanced")
(unbalanced
> (displayln "#invalid (syntax . too . many . dots)")
#invalid (syntax . too . many . dots)

This will also have the side-effect of allowing the prompt to be matched inside s-expressions.

The #:no-read-definitions can be useful if the first prompt could be part of an s-expression, for example using #lang reader "literal.rkt" from the docs:

#lang repltest #:no-read-definitions #:prompt-start-of-line reader "literal.rkt"
This > text > is > in > the > definitions
> 'first-prompt
'first-prompt
> data
"This > text > is > in > the > definitions"