Remove default .once in singular matchers

[inkstak]

The previous situation

Implicitely, both matchers enqueue_sidekiq_job and have_enqueued_sidekiq_job matched that exactly only one job was enqueued.

it "asserts that only job has been enqueued" do
  expect {
    SampleJob.perform_async
  }.to enqueue_sidekiq_job(SampleJob)
end

A plural (and undocumented) version of both matchers was available to not care about of how many jobs were enqueued.

it "asserts that at least one jobs has been enqueued" do
  expect {
    SampleJob.perform_async
    SampleJob.perform_async
  }.to enqueue_sidekiq_jobs(SampleJob)
end

The problem

Using this singular matcher may be confusing, especially when using negative assertions:

it "succeed, but it smells like a false positive" do
  expect {
    SampleJob.perform_async
    SampleJob.perform_async
  }.not_to enqueue_sidekiq_job(SampleJob)
end

The solution

The implicit .once option will be removed. Both singular and plural matchers are now aliased.
If you want to verify that only one and exactly only one job has been enqueued, you have to do it explicitely :

it do
  expect {
    SampleJob.perform_async
  }.to enqueue_sidekiq_job(SampleJob).once
end

it do
  expect {
    SampleJob.perform_async
    SampleJob.perform_async
  }.not_to enqueue_sidekiq_job(SampleJob).once
end

This solution should not break existing specs, except ambiguous negative assertions.