Add mutant

Author: ipepe

.mutant.yml

@@ -0,0 +1,2 @@
+---
+integration: rspec

Gemfile

@@ -1,4 +1,8 @@
 source 'https://rubygems.org'
 git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 
+gem 'mutant'
+gem 'mutant-rspec'
+gem 'mutant-license', source: 'https://oss:IG9NKHkepT1VE6CyvJiYH14GUsCHPtog@gem.mutant.dev'
+
 gemspec name: 'jsonapi_parameters'

Rakefile

@@ -18,3 +18,119 @@ require 'bundler/gem_tasks'
 require 'rspec/core/rake_task'
 
 task :default => :spec
+
+
+# Pass a match expression as an optional argument to only run mutant
+# on classes that match. Example: `rake mutant TaxTribs::ZendeskSender`
+#
+task :mutant do
+  current_ci_branch = ENV['CIRCLE_BRANCH']
+
+  # Do not run mutant on CI master or develop branches.
+  # Mutant will only run on pull requests against modified files.
+  #
+  if %w(master develop).include?(current_ci_branch)
+    puts "> CI #{current_ci_branch} branch -- mutant will not run"
+    exit
+  end
+
+  mutation_type = ARGV[1]
+
+  vars = 'RAILS_ENV=test NOCOVERAGE=true'.freeze
+  flags = ['--use rspec', '--fail-fast']
+
+  # When running on CI, a very high number of concurrent jobs seem to make some
+  # mutations fail randomly. Reducing the number of jobs minimise this problem.
+  flags.push('--jobs 24') if current_ci_branch
+
+  # This is to avoid running the mutant with flag `--since master` when
+  # we are already on master, as otherwise it will not work as expected.
+  current_branch = current_ci_branch || `git rev-parse --abbrev-ref HEAD`
+
+  if mutation_type == 'master'
+    puts "> current branch: #{current_branch}"
+
+    if current_branch != 'master'
+      puts "> running complete mutant testing on all changes since 'origin/master'"
+      flags.push('--since origin/master')
+    else
+      # As we are already in master, let's not use the --since, and fallback to
+      # running the quick randomised sample
+      puts "> already on master, overriding --since flag"
+      mutation_type = nil
+    end
+  end
+
+  unless system("#{vars} mutant #{flags.join(' ')} #{classes_to_mutate(mutation_type).join(' ')}")
+    raise 'Mutation testing failed'
+  end
+
+  exit
+end
+
+private
+
+def classes_to_mutate(option)
+
+  case option
+  when nil
+    # Quicker run, reduced testing scope (random sample), default option
+    puts '> running quick sample mutant testing'
+    form_objects.sample(5) + decision_trees_and_services.sample(3) + models
+  when 'all', 'master'
+    # Complete coverage (very long run time) or only changed classes
+    puts '> running complete mutant testing'
+    form_objects + decision_trees_and_services + models + jobs
+  else
+    # Individual class testing, very quick
+    # we'll take all arguments after the first (which is 'mutant')
+    _foo, *classes = ARGV
+    classes
+  end
+end
+
+# Classes that, for different reasons, mutant can't cope with or gives
+# false positives (for example, due to multi-threading tests, etc.)
+#
+def excluded_constants
+  [
+    C100App::PaymentsFlowControl,
+  ].freeze
+end
+
+# As the current models are just empty shells for ActiveRecord relationships,
+# and we don't even have corresponding spec tests for those, there is no point
+# in including these in the mutation test, and thus we can save some time.
+# Only include in this collection the models that matter and have specs.
+#
+def models
+  %w(
+    C100Application
+    Applicant
+    Solicitor
+    User
+    PaymentIntent
+    CompletedApplicationsAudit
+  ).freeze
+end
+
+# Everything inheriting from `BaseForm` and inside namespace `Steps`
+# i.e. all classes in `/app/forms/steps/**/*`
+#
+def form_objects
+  BaseForm.descendants.map(&:name).grep(/^Steps::/)
+end
+
+# Everything inside `C100App` namespace, unless included in `#excluded_constants`
+# i.e. all classes in `/app/services/c100_app/*`
+#
+def decision_trees_and_services
+  C100App.constants.map { |symbol| C100App.const_get(symbol) } - excluded_constants
+end
+
+# Everything inheriting from `ApplicationJob`
+# i.e. all jobs in `/app/jobs/*`
+#
+def jobs
+  ApplicationJob.descendants
+end

bin/ci

@@ -4,3 +4,4 @@ set -e
 
 bundle exec bin/quality
 bundle exec bin/spec
+bundle exec bin/mutant

bin/mutant

@@ -0,0 +1,5 @@
+#!/usr/bin/env sh
+
+set -e
+
+bundle exec mutant