Ensure user-specified error classes take priority

[kinbiko]

Goal

In v1.4.0 we introduced a bug when changing the order of the error and
other metadata in notifier.Notify. This commit rectifies this by
explicitly checking that the error class has not been set previously
before setting it automatically.

Changeset

Added

• Check to see if the error class has already been set before assigning the default error class from the error itself.

Changed

• Notify test to catch this bug if it should occur in future releases.

Linked issues

Fixes #98

Testing

@Cawllec could you have a look and see if you think we need another set of maze tests for this case?

Review

For the submitter, initial self-review:

• Commented on code changes inline explain the reasoning behind the approach
• Reviewed the test cases added for completeness and possible points for discussion
• A changelog entry was added for the goal of this pull request
• Check the scope of the changeset - is everything in the diff required for the pull request?
• This pull request is ready for:
  • Initial review of the intended approach, not yet feature complete
  • Structural review of the classes, functions, and properties modified
  • Final review

For the pull request reviewer(s), this changeset has been reviewed for:

• Consistency across platforms for structures or concepts added or modified
• Consistency between the changeset and the goal stated above
• Internal consistency with the rest of the library - is there any overlap between existing interfaces and any which have been added?
• Usage friction - is the proposed change in usage cumbersome or complicated?
• Performance and complexity - are there any cases of unexpected O(n^3) when iterating, recursing, flat mapping, etc?
• Concurrency concerns - if components are accessed asynchronously, what issues will arise
• Thoroughness of added tests and any missing edge cases
• Idiomatic use of the language

[mikeewhite]

LGTM

[klautcomputing]

I just ran into this, any idea when you are going to release it?

[kinbiko]

hi @klautcomputing,

We're aiming to release it early next week. Thanks for your patience!