which property
A description of the way that actual failed to meet the expectation.
An expectation can provide extra detail, or focus attention on a specific part of the value. For instance when comparing multiple elements in a collection, the rejection may describe that the value "has an unequal value at index 3".
Lines should be separate values in the iterable, if any element contains a newline it may cause problems with indentation in the output.
When provided, this is printed following a "Which: " label at the end of the output for the failure message.
Implementation
final Iterable<String>? which;