Firstly, thank you for this gem and your work!

Testing verbose level :compact I discovered that the exception description is meant to be displayed in the slack message, unfortunately this is not the case. To test this I used the following script:

require 'resque/failure/slack'
Resque::Failure::Slack.configure do |config|
  config.channel = ''
  config.token = ''
  config.level = :compact
end
resque_slack = Resque::Failure::Slack.new(
  ArgumentError,
  'JobName',
  'high',
  {
    data: []
  }
)
resque_slack.text

# Returns
# "JobName failed processing high\nPayload:\n  {:data=>[]}\n\n"

Proposed Changes

Since msg_exception last line returns nil for level :compact, I suggest that return str is inserted at the end of the function to ensure both levels :verbose and :compact work as expected:

Before:

def msg_exception(backtrace)
  str = "Exception:\n#{exception}"
  str += "\n#{exception.backtrace.map { |l| '  ' + l }.join('\n')}" if backtrace
end

After

def msg_exception(backtrace)
  str = "Exception:\n#{exception}"
  str += "\n#{exception.backtrace.map { |l| '  ' + l }.join('\n')}" if backtrace
  return str
end

Re-running the script now returns the following:

# "JobName failed processing high\nPayload:\n  {:data=>[]}\nException:\nArgumentError\n"

Please let me know if you would like me to raise PR for these changes.

ruby - 2.5.1
rails - 5.2.2
resque - 1.27

Neat tool and we are going to try it out. Looks like we had to add full API permissions for chat:write to our Slack App. But now Slack supports (encourages?) webhooks for writing messages. That would be a great option to have if this gets updated at some point.

In the latest version resque complains
*** Received exception when reporting failure: #<NameError: uninitialized constant Resque::Failure::Slack::Notification>
It comes because resque/failure/notification isn't required anywhere except spec_helper.

Hey, Great Gem!
Well, after I used this gem, there will be no failed jobs show on http://localhost:3000/resque/failed here, right?
Is this meant to work like this?

Thank you