fix: Internal Referencing for Increment Dot Notation

[dplewis]

This PR is building upon #1219, together they solve the following issues.

There was a internal referencing issue that resulted in the increment to happen every time you get the attributes
Lucky this .get returns the proper value so clients aren't affected. (Fixed in this PR).

const obj = new TestObject();
obj.set('objectField', { number: 5 });
obj.increment('objectField.number', 15);
console.log(obj.attributes); // Internally number is 20
console.log(obj.attributes); // Internally number is 35
console.log(obj.attributes); // Internally number is 50

When you save with increment there is an extra attribute returned from _handleSaveResponse (Fixed in #1219)

{
  objectField: { number: 20 },
  createdAt: 2020-11-11T17:35:48.317Z,
  updatedAt: 2020-11-11T17:35:48.337Z,
  'objectField.number': 15 // Has been removed
}

When saving after using increment nested, the full object isn't returned. (Fixed in #1219)

{
  objectField: { number: 20, letter: 'a' }, // Didn't return 'a' before when using increment nested
  createdAt: 2020-11-11T17:35:48.317Z,
  updatedAt: 2020-11-11T17:35:48.337Z,
}

• Also adds error listener to test server. Useful for catching 'Address in Use` errors.

When merged with the server this will work in beforeSave / afterSaves hooks.

[codecov]

Codecov Report

Merging #1255 (3268681) into master (f443834) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1255   +/-   ##
=======================================
  Coverage   99.98%   99.98%           
=======================================
  Files          57       57           
  Lines        5403     5405    +2     
  Branches     1199     1199           
=======================================
+ Hits         5402     5404    +2     
  Misses          1        1           

Impacted Files	Coverage Δ
src/ObjectStateMutations.js	100.00% <100.00%> (ø)
src/ParseObject.js	100.00% <100.00%> (ø)

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[davimacedo]

It looks good but I believe you should revert the changes in the package-lock, right?