Rubocop fixes and test

.rubocop.yml

@@ -1,3 +1,7 @@
 AllCops:
-  TargetRubyVersion: 3.2
+  TargetRubyVersion: 2.6
+  NewCops: enable
 
+Metrics/BlockLength:
+  Exclude:
+    - spec/cron_calc_spec.rb

cron_calc.gemspec

@@ -17,6 +17,7 @@ Gem::Specification.new do |spec|
   spec.metadata['homepage_uri'] = spec.homepage
   spec.metadata['source_code_uri'] = 'https://github.com/mizinsky/cron_calc'
   spec.metadata['changelog_uri'] = 'https://github.com/mizinsky/cron_calc/blob/main/CHANGELOG.md'
+  spec.metadata['rubygems_mfa_required'] = 'true'
 
   # Specify which files should be added to the gem when it is released.
   # The `git ls-files -z` loads the files in the RubyGem that have been added into git.

lib/cron_calc.rb

@@ -3,13 +3,17 @@
 require_relative 'cron_calc/version'
 require 'time'
 
+# The CronCalc is gem-wrapper module for the Parser class
 module CronCalc
   class Error < StandardError; end
 
   def self.new(cron_string, period)
     Parser.new(cron_string, period)
   end
 
+  # The Parser class provides functionality to parse and calculate occurrences
+  # of cron jobs within a given time period. It interprets cron strings and
+  # calculates when cron jobs will occur
   class Parser
     attr_reader :cron_string, :cron_parts, :period
 
@@ -54,6 +58,7 @@ def parse_cron_expression
       %i[minutes hours days months].map { |unit| parse_cron_part(unit) } << (period.min.year..period.max.year).to_a
     end
 
+    # rubocop:disable Metrics
     def parse_cron_part(time_unit)
       range = RANGE[time_unit]
       part = cron_parts[time_unit]
@@ -71,9 +76,12 @@ def parse_cron_part(time_unit)
         [part.to_i]
       end
     end
+    # rubocop:enable Metrics
 
     def cron_string_valid?
+      # rubocop:disable Layout/LineLength
       regex = %r{\A(\*|([0-5]?\d)(,([0-5]?\d))*|(\*/\d+)|(\d+-\d+)) (\*|([01]?\d|2[0-3])(,([01]?\d|2[0-3]))*|(\*/\d+)|(\d+-\d+)) (\*|([12]?\d|3[01])(,([12]?\d|3[01]))*|(\*/\d+)|(\d+-\d+)) (\*|([1-9]|1[0-2])(,([1-9]|1[0-2]))*|(\*/\d+)|(\d+-\d+)) \*\z}
+      # rubocop:enable Layout/LineLength
       cron_string.match?(regex)
     end
   end

spec/cron_calc_spec.rb

@@ -102,7 +102,7 @@
       let(:period) { Time.new(2023, 1, 1)..Time.new(2023, 1, 2) }
 
       it do
-        expect { subject }.to raise_error(RuntimeError, 'Cron expression is not supported or invalid')
+        expect { subject }.to raise_error(RuntimeError, 'Cron expression is not supported or invalid test')
       end
     end