From 719cc67769776ac3211442f65c0ec8323d2fccbc Mon Sep 17 00:00:00 2001
From: Chris Zetter <253059100+zetter-rpf@users.noreply.github.com>
Date: Tue, 8 Sep 2026 16:09:15 +0100
Subject: [PATCH 1/2] Reduce likelyhood of random number conflicts

By using the non-secure random generator, and caching the class that may be forked in Puma, we're making conflicts more likely.

This is still a possibility of collisions - we've almost used 1% of available codes, however this might reduce the change.

I've removed the random number seed as part of this - SecureRandom can't be seeded in the same way. Looking at the commit history, this was a tool to help make test runs more deterministic but isn't required. If we do, we should add the ability to swap out random number generators.
---
 lib/for_education_code_generator.rb           | 8 +++-----
 spec/lib/for_education_code_generator_spec.rb | 4 ++--
 spec/support/for_education_code_generator.rb  | 8 --------
 3 files changed, 5 insertions(+), 15 deletions(-)
 delete mode 100644 spec/support/for_education_code_generator.rb

diff --git a/lib/for_education_code_generator.rb b/lib/for_education_code_generator.rb
index f0da81148..88257258d 100644
--- a/lib/for_education_code_generator.rb
+++ b/lib/for_education_code_generator.rb
@@ -1,14 +1,12 @@
 # frozen_string_literal: true
 
+require 'securerandom'
+
 class ForEducationCodeGenerator
   MAX_CODE = 1_000_000
 
-  cattr_accessor :random
-
-  self.random ||= Random.new
-
   def self.generate
-    number = random.rand(MAX_CODE)
+    number = SecureRandom.random_number(MAX_CODE)
     code = format('%06d', number)
 
     code.match(/(\d\d)(\d\d)(\d\d)/) do |m|
diff --git a/spec/lib/for_education_code_generator_spec.rb b/spec/lib/for_education_code_generator_spec.rb
index 2da0f6e1e..d8956b66e 100644
--- a/spec/lib/for_education_code_generator_spec.rb
+++ b/spec/lib/for_education_code_generator_spec.rb
@@ -4,8 +4,8 @@
 
 RSpec.describe ForEducationCodeGenerator do
   describe '.generate' do
-    it 'uses Random#rand to generate a random number up to the maximum' do
-      allow(described_class.random).to receive(:rand).with(ForEducationCodeGenerator::MAX_CODE).and_return(123)
+    it 'uses SecureRandom to generate a random number up to the maximum' do
+      allow(SecureRandom).to receive(:random_number).with(ForEducationCodeGenerator::MAX_CODE).and_return(123)
 
       expect(described_class.generate).to eq('00-01-23')
     end
diff --git a/spec/support/for_education_code_generator.rb b/spec/support/for_education_code_generator.rb
deleted file mode 100644
index 53c74df24..000000000
--- a/spec/support/for_education_code_generator.rb
+++ /dev/null
@@ -1,8 +0,0 @@
-# frozen_string_literal: true
-
-RSpec.configure do |config|
-  config.before(:suite) do
-    Rails.logger.debug { "ForEducationCodeGenerator randomized with seed #{config.seed}" }
-    ForEducationCodeGenerator.random = Random.new(config.seed)
-  end
-end

From ebc1fd6689a4e40ab740001209204f47e08adab3 Mon Sep 17 00:00:00 2001
From: Chris Zetter <253059100+zetter-rpf@users.noreply.github.com>
Date: Tue, 8 Sep 2026 16:19:25 +0100
Subject: [PATCH 2/2] remove spec that has 1 in 1000000 chance of failing

---
 spec/lib/for_education_code_generator_spec.rb | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/spec/lib/for_education_code_generator_spec.rb b/spec/lib/for_education_code_generator_spec.rb
index d8956b66e..030cb231f 100644
--- a/spec/lib/for_education_code_generator_spec.rb
+++ b/spec/lib/for_education_code_generator_spec.rb
@@ -13,9 +13,5 @@
     it 'generates a string containing 3 pairs of digits' do
       expect(described_class.generate).to match(/\d\d-\d\d-\d\d/)
     end
-
-    it 'generates a different code each time' do
-      expect(described_class.generate).not_to eq(described_class.generate)
-    end
   end
 end