Explain diff gutter symbols

Please see this comment: https://github.com/avajs/ava/issues/1558#issuecomment-469031454

Original issue follows.

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Description

When using t.snapshot(foo) and foo does not match the snapshot, the diff that is shown uses - to indicate the new foo values and + to show the old foo values.

This is unintuitive.

I believe the problem may be at https://github.com/avajs/ava/blob/14f7095d25abc5ffbff7efd7db962eaf5e86daab/lib/assert.js#L321

Test Source

import test from 'ava'
test('snapshot diff', t => {
  t.snapshot(`\n${Date.now()}\n`, 'the - value should be less than the + value')
})

Environment

Latest stable ava on OS X

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Submitted pull Requests

• #2199 Added gutter descriptors

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[nesbocaj]

@arteniioleg Jest should only be confusing if you assume the colors have the same purpose, they don’t. In Git the colors signifies changes, with green signifying added/new, and red, removed/old. Whereas in Jest the colors signify (the assumed) correctness of the value, with green signifying correct, and red, incorrect.

In both instances the preceding symbol signifies changes, with + signifying added/new, and -, removed/old.

It’s also worth noting that Jest goes quite far in explaining (or at least trying to explain) this concept to the user.

[wmertens]

Yes, the way Jest does it looks good!

On Thu, Mar 1, 2018 at 12:53 PM rzec-r7 [e-mail] wrote:

@novemberborn https://github.com/novemberborn any update on this? I have been tripped up by the + / - difference with AVA so many times.

I think what @nesbocaj https://github.com/nesbocaj said makes sense. For me the colors are not as important as the - / + and since snapshots are tests that are just diffing 2 values, it make the most sense to have the - be the existing value in the snapshot and the + be the new value from the test (I have not opinion on the colors, probably makes to to just match what jest does).

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