Expose exception message via #to_s

[tijmenb]

What problem does the pull request solve?

Exceptions in Ruby return the exception message when calling #to_s on it:

> irb
irb(main):001:0> StandardError.new("Hi").to_s
=> "Hi"

Because this is default behaviour, libraries sometimes depend on to_s to get a readable version of the exception message. For example, the Sentry client does it to give the exception a name:

https://github.com/getsentry/raven-ruby/blob/065cf973cb0ad3672d0d213e80b6e8a9a8e6f8cb/lib/raven/event.rb#L144

Currently, Sentry reports do not show the error message set when raising the exception - it only displays Notifications::Client::BadRequestError:

This is because we’re only defining RequestError#message. This is apparently not the same as initialising an exception with a message, as you can see here:

> be rails c
Loading development environment (Rails 6.0.2.1)
[1] pry(main)>
Notifications::Client::BadRequestError.new(OpenStruct.new(code: "hey", body: {errors: [{error: "BadRequestError", message: "Can’t send to this recipient using a team-only API key"}] }.to_json )).to_s
=> "Notifications::Client::BadRequestError"
[2] pry(main)>
Notifications::Client::BadRequestError.new(OpenStruct.new(code: "hey", body: {errors: [{error: "BadRequestError", message: "Can’t send to this recipient using a team-only API key"}] }.to_json )).message 
=> "BadRequestError: Can’t send to this recipient using a team-only API key"

The issue was introduced in #73 / #72, which removed the explicit to_s method.

This commit fixes the issue by constructing the message in the constructor. Note that we’ve renamed the message method, but calling e.message still works because it’s part of the exception interface.

Another option would be to add the to_s method back (like we experimented with in DFE-Digital/apply-for-teacher-training#1024), but this solution seems the most Ruby-esque and relies on less knowledge of Exception internals.

After DFE-Digital/apply-for-teacher-training#1024, the exceptions are properly reported:

Before	After

This change is backwards compatible.

Checklist

• I’ve used the pull request template
• I’ve written unit tests for these changes
• I’ve updated the documentation (in DOCUMENTATION.md)
• I’ve bumped the version number (in lib/notifications/client/version.rb)

[leohemsted]

@tijmenb thanks for this! It seems sensible, and great PR description/context. I'll get this deployed now

[tijmenb]

Thanks @leohemsted !

[benlovell]

Just came here to add this myself then realised @tijmenb got it in before me! Thanks <3