Test failures are reported with wrong line number

When a test failure gets reported, it gets assigned with the line number of the `facts` call. If you have a long segment of arrow assertions inside the facts block, this is not too helpful. It'd be better if either the line of the arrow or the line of the preceding form would be reported.

Start by locating the implementation of the facts block and arrow assertions, then reproduce a failure in a long facts segment to inspect how its source line is selected. Done means failures report the arrow line or the preceding form instead of the facts call line.

Written by the indexing model from the issue text.