Add spec for BatchBuilder contention

Previously we had an issue where BatchBuilder would create the wrong
number of promotion codes if it encountered a conflict. Out specs didn't
catch this.

This commit adds an additional spec which runs the BatchBuilder with
settings that make it extremely likely that there will a conflict: from
a space of 100 possible codes (00 to 99) we generate 50.

An online birthday problem calculator tells me this is 99.99997%
likely that the generator will encounter at least one conflict. That
seems plenty. I haven't verified this, but intuitively it seems very
likely.

core/spec/models/spree/promotion_code/batch_builder_spec.rb

@@ -4,11 +4,12 @@
  let(:promotion) { create(:promotion) }
  let(:base_code) { "abc" }
  let(:options) { {} }
+ let(:number_of_codes) { 10 }
  let(:promotion_code_batch) do
  Spree::PromotionCodeBatch.create!(
  promotion_id: promotion.id,
  base_code: base_code,
- number_of_codes: 10,
+ number_of_codes: number_of_codes,
  email: "[email protected]"
  )
  end
@@ -54,6 +55,22 @@
  expect(promotion_code_batch.state).to eq("completed")
  end
  end
+
+ context "with likely code contention" do
+ let(:number_of_codes) { 50 }
+ let(:options) do
+ {
+ batch_size: 10,
+ sample_characters: (0..9).to_a.map(&:to_s),
+ random_code_length: 2
+ }
+ end
+
+ it "creates the correct number of codes" do
+ subject.build_promotion_codes
+ expect(promotion.codes.size).to eq(number_of_codes)
+ end
+ end
  end
 
  describe "#join_character" do