Snapshot diff gutters feel counterintuitive

[gautaz]

Hello,

Looking at #1558, the way diff gutter symbol is interpreted has already been an issue.

Currently when a snapshot test fails, the console displays something close to the following:

  ...
- new snapshot value
+ recorded snapshot value
  ...

Most of our developers (myself included) are having a hard time interpreting this the right way (i.e. + feels like the value for the new snapshot).

Hence this little poll to know if our brains here are just badly connected or if it is a more global issue.