Snapshot ids can collide with test names

[ninevra]

What you're trying to do

I'm just testing edge cases in hopes of better understanding the code. This isn't likely to be important to anyone's use case.

What happened

If a snapshot has an id that matches a test name, it compares against the first snapshot from that test.

What you expected to happen

This should probably either:

• Throw an error, like duplicate test titles do.
• Report an error by some other means.
• Namespace snapshot ids separately from test names. That would probably require changes to the snapshot binary format.

The existing behavior could be used intentionally, but I can't think of a good reason to do so.

Sample code

const test = require('ava');

test('a name', t => {
  t.snapshot('one', 'a snapshot with no id');
  t.snapshot('two', {id: 'a name'});
});

This produces:

  a name

  test.js:5

   4:   t.snapshot('one', 'a snapshot with no id');
   5:   t.snapshot('two', {id: 'a name'});         
   6: });                                          

  Did not match snapshot

  Difference:

  - 'two'
  + 'one'

  › test.js:5:5

  ─

  1 test failed

The snapshot report looks like:

# Snapshot report for `test.js`

The actual snapshot is saved in `test.js.snap`.

Generated by [AVA](https://avajs.dev).

## a name

> a snapshot with no id

    'one'

Configuration

AVA v3.15.0.

No AVA configuration.

Invoking AVA as npx ava or npx ava --update-snapshots.

[novemberborn]

Perhaps we should remove this feature?

[novemberborn]

https://github.com/avajs/ava/issues/2669