Add ordering mutations

[fix #1442]

lib/mutant/parallel/connection.rb

@@ -21,11 +21,11 @@ class Reader
  attr_reader :log
 
  def error
- @errors.first
+ Util.max_one(@errors)
  end
 
  def result
- @results.first
+ Util.max_one(@results)
  end
 
  def initialize(*)
@@ -96,7 +96,7 @@ def advance_result
  end
 
  def length
- @lengths.first
+ Util.max_one(@lengths)
  end
 
  def advance_log

lib/mutant/util.rb

@@ -19,5 +19,23 @@ def self.one(array)
  fail SizeError, "expected size to be exactly 1 but size was #{array.size}"
  end
  end
+
+ # Return only element in array if it contains max one member
+ #
+ # @param array [Array]
+ #
+ # @return [Object] first entry
+ # @return [nil] if empty
+ #
+ # rubocop:disable Lint/EmptyInPattern
+ def self.max_one(array)
+ case array
+ in []
+ in [value]
+ value
+ else
+ fail SizeError, "expected size to be max 1 but size was #{array.size}"
+ end
+ end
  end # Util
 end # Mutant

spec/unit/mutant/util_spec.rb

@@ -53,3 +53,55 @@ def apply
  end
  end
 end
+
+RSpec.describe Mutant::Util, '.max_one' do
+ let(:item) { instance_double(Object) }
+
+ def apply
+ described_class.max_one(array)
+ end
+
+ context 'when array has exactly one element' do
+ context 'and that element is nil' do
+ let(:array) { [nil] }
+
+ it 'returns nil' do
+ expect(apply).to be(nil)
+ end
+ end
+
+ context 'and that element is false' do
+ let(:array) { [false] }
+
+ it 'returns false' do
+ expect(apply).to be(false)
+ end
+ end
+
+ context 'and that element is a regular object' do
+ let(:array) { [item] }
+
+ it 'returns first element' do
+ expect(apply).to be(item)
+ end
+ end
+ end
+
+ context 'when array is empty' do
+ let(:array) { [] }
+
+ it 'returns nil' do
+ expect(apply).to be(nil)
+ end
+ end
+
+ context 'when array has more than one element' do
+ let(:array) { [1, 2] }
+
+ it 'raises expected error' do
+ expect { apply }
+ .to raise_error(described_class::SizeError)
+ .with_message('expected size to be max 1 but size was 2')
+ end
+ end
+end