Optimize range iteration

For loops support a range syntax for iterating a fixed number of times,
which looks like this.

```liquid
{% for i in range (1..100) %}
        ...
{% endfor %}
```

Previously, we converted these ranges to arrays using `to_a`, which
initialized an array containing each number in the range. Since all we
use these ranges for is iteration, this is far less efficient than
using a range iterator.

Doing this means that iterating over ranges now takes O(1) rather than O(n)
memory. See the PR for more benchmarks.

* Remove to_a cast on ranges
* Add ReversableRange iterator
* Add custom range-specific slicing logic

.rubocop.yml

@@ -1,4 +1,6 @@
-inherit_from: ./.rubocop_todo.yml
+inherit_from:
+  - .rubocop_todo.yml
+  - ./.rubocop_todo.yml
 
 AllCops:
   Exclude:
@@ -29,7 +31,7 @@ Lint/ParenthesesAsGroupedExpression:
 Lint/UnusedBlockArgument:
   Enabled: false
 
-Lint/EndAlignment:
+Layout/EndAlignment:
   EnforcedStyleAlignWith: variable
 
 Lint/UnusedMethodArgument:
@@ -59,7 +61,7 @@ Style/BracesAroundHashParameters:
 Style/NumericLiterals:
   Enabled: false
 
-Layout/SpaceInsideBrackets:
+Layout/SpaceInsideArrayLiteralBrackets:
   Enabled: false
 
 Layout/SpaceBeforeBlockBraces:
@@ -71,7 +73,10 @@ Style/Documentation:
 Style/ClassAndModuleChildren:
   Enabled: false
 
-Style/TrailingCommaInLiteral:
+Style/TrailingCommaInArrayLiteral:
+  Enabled: false
+
+Style/TrailingCommaInHashLiteral:
   Enabled: false
 
 Layout/IndentHash:
@@ -104,7 +109,7 @@ Style/SymbolLiteral:
 Performance/Count:
   Enabled: false
 
-Style/ConstantName:
+Naming/ConstantName:
   Enabled: false
 
 Layout/CaseIndentation:
@@ -122,6 +127,6 @@ Style/TrivialAccessors:
 Style/WordArray:
   Enabled: false
 
-Style/MethodName:
+Naming/MethodName:
   Exclude:
     - 'example/server/liquid_servlet.rb'

.rubocop_todo.yml

@@ -1,14 +1,22 @@
 # This configuration was generated by
 # `rubocop --auto-gen-config`
-# on 2019-02-03 21:12:39 +0530 using RuboCop version 0.49.1.
+# on 2019-03-19 11:04:37 -0400 using RuboCop version 0.53.0.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
 # versions of RuboCop, may require this file to be generated again.
 
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: Include, TreatCommentsAsGroupSeparators.
+# Include: **/*.gemspec
+Gemspec/OrderedDependencies:
+  Exclude:
+    - 'liquid.gemspec'
+
 # Offense count: 5
 # Cop supports --auto-correct.
-# Configuration parameters: EnforcedStyle, SupportedStyles.
+# Configuration parameters: EnforcedStyle.
 # SupportedStyles: auto_detection, squiggly, active_support, powerpack, unindent
 Layout/IndentHeredoc:
   Exclude:
@@ -17,7 +25,7 @@ Layout/IndentHeredoc:
 
 # Offense count: 6
 # Cop supports --auto-correct.
-# Configuration parameters: EnforcedStyle, SupportedStyles.
+# Configuration parameters: EnforcedStyle.
 # SupportedStyles: symmetrical, new_line, same_line
 Layout/MultilineMethodCallBraceLayout:
   Exclude:
@@ -26,38 +34,65 @@ Layout/MultilineMethodCallBraceLayout:
 
 # Offense count: 2
 # Cop supports --auto-correct.
-# Configuration parameters: EnforcedStyle, SupportedStyles.
+# Configuration parameters: EnforcedStyle.
 # SupportedStyles: runtime_error, standard_error
 Lint/InheritException:
   Exclude:
     - 'lib/liquid/interrupts.rb'
 
-# Offense count: 51
+# Offense count: 1
+# Configuration parameters: CheckForMethodsWithNoSideEffects.
+Lint/Void:
+  Exclude:
+    - 'lib/liquid/parse_context.rb'
+
+# Offense count: 54
 Metrics/AbcSize:
   Max: 56
 
-# Offense count: 11
+# Offense count: 12
 Metrics/CyclomaticComplexity:
   Max: 12
 
-# Offense count: 639
+# Offense count: 112
-# Configuration parameters: AllowHeredoc, AllowURI, URISchemes, IgnoreCopDirectives, IgnoredPatterns.
-# URISchemes: http, https
-Metrics/LineLength:
-  Max: 294
-
-# Offense count: 108
 # Configuration parameters: CountComments.
 Metrics/MethodLength:
   Max: 37
 
-# Offense count: 7
+# Offense count: 8
 Metrics/PerceivedComplexity:
   Max: 11
 
+# Offense count: 52
+# Configuration parameters: Blacklist.
+# Blacklist: END, (?-mix:EO[A-Z]{1})
+Naming/HeredocDelimiterNaming:
+  Exclude:
+    - 'test/integration/assign_test.rb'
+    - 'test/integration/capture_test.rb'
+    - 'test/integration/trim_mode_test.rb'
+
+# Offense count: 23
+# Configuration parameters: MinNameLength, AllowNamesEndingInNumbers, AllowedNames, ForbiddenNames.
+# AllowedNames: io, id
+Naming/UncommunicativeMethodParamName:
+  Exclude:
+    - 'example/server/example_servlet.rb'
+    - 'lib/liquid/condition.rb'
+    - 'lib/liquid/context.rb'
+    - 'lib/liquid/standardfilters.rb'
+    - 'lib/liquid/tags/if.rb'
+    - 'lib/liquid/utils.rb'
+    - 'lib/liquid/variable.rb'
+    - 'test/integration/filter_test.rb'
+    - 'test/integration/standard_filter_test.rb'
+    - 'test/integration/tags/for_tag_test.rb'
+    - 'test/integration/template_test.rb'
+    - 'test/unit/condition_unit_test.rb'
+
 # Offense count: 10
 # Cop supports --auto-correct.
-# Configuration parameters: EnforcedStyle, SupportedStyles.
+# Configuration parameters: EnforcedStyle.
 # SupportedStyles: prefer_alias, prefer_alias_method
 Style/Alias:
   Exclude:
@@ -69,14 +104,23 @@ Style/Alias:
     - 'lib/liquid/tags/include.rb'
     - 'lib/liquid/variable.rb'
 
+# Offense count: 22
+Style/CommentedKeyword:
+  Enabled: false
+
 # Offense count: 1
 # Cop supports --auto-correct.
-# Configuration parameters: EnforcedStyle, SupportedStyles, SingleLineConditionsOnly, IncludeTernaryExpressions.
+# Configuration parameters: EnforcedStyle, SingleLineConditionsOnly, IncludeTernaryExpressions.
 # SupportedStyles: assign_to_condition, assign_inside_condition
 Style/ConditionalAssignment:
   Exclude:
     - 'lib/liquid/errors.rb'
 
+# Offense count: 1
+Style/DateTime:
+  Exclude:
+    - 'test/unit/context_unit_test.rb'
+
 # Offense count: 2
 # Cop supports --auto-correct.
 Style/EmptyCaseCondition:
@@ -86,7 +130,7 @@ Style/EmptyCaseCondition:
 
 # Offense count: 5
 # Cop supports --auto-correct.
-# Configuration parameters: EnforcedStyle, SupportedStyles.
+# Configuration parameters: EnforcedStyle.
 # SupportedStyles: compact, expanded
 Style/EmptyMethod:
   Exclude:
@@ -96,11 +140,28 @@ Style/EmptyMethod:
     - 'test/integration/tags/include_tag_test.rb'
     - 'test/unit/context_unit_test.rb'
 
+# Offense count: 3
+# Cop supports --auto-correct.
+Style/Encoding:
+  Exclude:
+    - 'lib/liquid/version.rb'
+    - 'liquid.gemspec'
+    - 'test/integration/standard_filter_test.rb'
+
 # Offense count: 2
-# Configuration parameters: SupportedStyles.
+# Cop supports --auto-correct.
-# SupportedStyles: annotated, template
+Style/ExpandPathArguments:
+  Exclude:
+    - 'Rakefile'
+    - 'liquid.gemspec'
+
+# Offense count: 7
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: annotated, template, unannotated
 Style/FormatStringToken:
-  EnforcedStyle: template
+  Exclude:
+    - 'test/integration/filter_test.rb'
+    - 'test/integration/hash_ordering_test.rb'
 
 # Offense count: 14
 # Configuration parameters: MinBodyLength.
@@ -121,7 +182,7 @@ Style/GuardClause:
 
 # Offense count: 1
 # Cop supports --auto-correct.
-# Configuration parameters: EnforcedStyle, MinBodyLength, SupportedStyles.
+# Configuration parameters: EnforcedStyle, MinBodyLength.
 # SupportedStyles: skip_modifier_ifs, always
 Style/Next:
   Exclude:
@@ -129,7 +190,7 @@ Style/Next:
 
 # Offense count: 4
 # Cop supports --auto-correct.
-# Configuration parameters: AutoCorrect, EnforcedStyle, SupportedStyles.
+# Configuration parameters: AutoCorrect, EnforcedStyle.
 # SupportedStyles: predicate, comparison
 Style/NumericPredicate:
   Exclude:
@@ -166,14 +227,14 @@ Style/Semicolon:
 
 # Offense count: 7
 # Cop supports --auto-correct.
-# Configuration parameters: MinSize, SupportedStyles.
+# Configuration parameters: MinSize.
 # SupportedStyles: percent, brackets
 Style/SymbolArray:
   EnforcedStyle: brackets
 
 # Offense count: 2
 # Cop supports --auto-correct.
-# Configuration parameters: EnforcedStyle, SupportedStyles, AllowSafeAssignment.
+# Configuration parameters: EnforcedStyle, AllowSafeAssignment.
 # SupportedStyles: require_parentheses, require_no_parentheses, require_parentheses_when_complex
 Style/TernaryParentheses:
   Exclude:
@@ -188,7 +249,12 @@ Style/UnneededPercentQ:
 
 # Offense count: 1
 # Cop supports --auto-correct.
-# Configuration parameters: MaxLineLength.
 Style/WhileUntilModifier:
   Exclude:
     - 'lib/liquid/tags/case.rb'
+
+# Offense count: 640
+# Configuration parameters: AllowHeredoc, AllowURI, URISchemes, IgnoreCopDirectives, IgnoredPatterns.
+# URISchemes: http, https
+Metrics/LineLength:
+  Max: 294

.travis.yml

@@ -23,7 +23,6 @@ matrix:
     - rvm: jruby-head
 
 install:
-  - gem install rainbow -v 2.2.1
   - bundle install
 
 script: bundle exec rake

Gemfile

@@ -5,16 +5,19 @@ end
 
 gemspec
 
-gem 'stackprof', platforms: :mri
-
 group :benchmark, :test do
   gem 'benchmark-ips'
+  gem 'memory_profiler'
+
+  install_if -> { RUBY_PLATFORM !~ /mingw|mswin|java/ } do
+    gem 'stackprof'
+  end
 end
 
 group :test do
-  gem 'rubocop', '~> 0.49.0'
+  gem 'rubocop', '~> 0.53.0'
 
   platform :mri do
-    gem 'liquid-c', github: 'Shopify/liquid-c', ref: '9168659de45d6d576fce30c735f857e597fa26f6'
+    gem 'liquid-c', github: 'Shopify/liquid-c', ref: 'reversable-range'
   end
 end

History.md

@@ -1,5 +1,10 @@
 # Liquid Change Log
 
+## 4.0.3 / 2019-03-12
+
+### Fixed
+* Fix break and continue tags inside included templates in loops (#1072) [Justin Li]
+
 ## 4.0.2 / 2019-03-08
 
 ### Changed

Rakefile

@@ -85,6 +85,13 @@ namespace :profile do
   end
 end
 
+namespace :memory_profile do
+  desc "Run memory profiler"
+  task :run do
+    ruby "./performance/memory_profile.rb"
+  end
+end
+
 desc "Run example"
 task :example do
   ruby "-w -d -Ilib example/server/server.rb"

lib/liquid.rb

@@ -74,6 +74,7 @@ require 'liquid/condition'
 require 'liquid/utils'
 require 'liquid/tokenizer'
 require 'liquid/parse_context'
+require 'liquid/reversable_range'
 
 # Load all the tags of the standard library
 #

lib/liquid/block_body.rb

@@ -89,6 +89,7 @@ module Liquid
           break
         else # Other non-Block tags
           render_node_to_output(node, output, context)
+          break if context.interrupt? # might have happened through an include
         end
         idx += 1
       end
@@ -114,7 +115,7 @@ module Liquid
     end
 
     def check_resources(context, node_output)
-      context.resource_limits.render_length += node_output.length
+      context.resource_limits.render_length += node_output.bytesize
       return unless context.resource_limits.reached?
       raise MemoryError.new("Memory limits exceeded".freeze)
     end

lib/liquid/range_lookup.rb

@@ -6,7 +6,7 @@ module Liquid
       if start_obj.respond_to?(:evaluate) || end_obj.respond_to?(:evaluate)
         new(start_obj, end_obj)
       else
-        start_obj.to_i..end_obj.to_i
+        ReversableRange.new(start_obj.to_i, end_obj.to_i)
       end
     end
 
@@ -18,7 +18,7 @@ module Liquid
     def evaluate(context)
       start_int = to_integer(context.evaluate(@start_obj))
       end_int = to_integer(context.evaluate(@end_obj))
-      start_int..end_int
+      ReversableRange.new(start_int, end_int)
     end
 
     private

lib/liquid/reversable_range.rb

@@ -0,0 +1,77 @@
+module Liquid
+  class ReversableRange
+    include Enumerable
+
+    def initialize(min, max)
+      @min = min
+      @max = max
+      @reversed = false
+    end
+
+    def each
+      if reversed
+        index = max
+        while index >= min
+          yield index
+          index -= 1
+        end
+      else
+        index = min
+        while index <= max
+          yield index
+          index += 1
+        end
+      end
+    end
+
+    def reverse!
+      @reversed = !reversed
+      self
+    end
+
+    def empty?
+      max < min
+    end
+
+    def size
+      difference = max - min
+      if difference > 0
+        difference + 1
+      else
+        0
+      end
+    end
+
+    def load_slice(from, to = nil)
+      to ||= max
+      slice_max = [max, to].min
+      slice_min = [min, from].max
+      range = ReversableRange.new(slice_min, slice_max)
+      range.reverse! if reversed
+      range
+    end
+
+    def ==(other)
+      other.is_a?(self.class) &&
+        other.min == min &&
+        other.max == max &&
+        other.reversed == reversed
+    end
+
+    def to_s
+      if reversed
+        "#{max}..#{min}"
+      else
+        "#{min}..#{max}"
+      end
+    end
+
+    def to_liquid
+      self
+    end
+
+    protected
+
+    attr_reader :min, :max, :reversed
+  end
+end

lib/liquid/tags/assign.rb

@@ -37,7 +37,7 @@ module Liquid
 
     def assign_score_of(val)
       if val.instance_of?(String)
-        val.length
+        val.bytesize
       elsif val.instance_of?(Array) || val.instance_of?(Hash)
         sum = 1
         # Uses #each to avoid extra allocations.

lib/liquid/tags/capture.rb

@@ -25,7 +25,7 @@ module Liquid
     def render(context)
       output = super
       context.scopes.last[@to] = output
-      context.resource_limits.assign_score += output.length
+      context.resource_limits.assign_score += output.bytesize
       ''.freeze
     end
 

lib/liquid/tags/for.rb

@@ -124,26 +124,34 @@ module Liquid
       from = if @from == :continue
         offsets[@name].to_i
       else
-        context.evaluate(@from).to_i
+        from_value = context.evaluate(@from)
+        if from_value.nil?
+          0
+        else
+          Utils.to_integer(from_value)
+        end
       end
 
       collection = context.evaluate(@collection_name)
-      collection = collection.to_a if collection.is_a?(Range)
 
-      limit = context.evaluate(@limit)
+      limit_value = context.evaluate(@limit)
-      to = limit ? limit.to_i + from : nil
+      to = if limit_value.nil?
+        nil
+      else
+        Utils.to_integer(limit_value) + from
+      end
 
       segment = Utils.slice_collection(collection, from, to)
       segment.reverse! if @reversed
 
-      offsets[@name] = from + segment.length
+      offsets[@name] = from + segment.size
 
       segment
     end
 
     def render_segment(context, segment)
       for_stack = context.registers[:for_stack] ||= []
-      length = segment.length
+      length = segment.size
 
       result = ''
 

lib/liquid/utils.rb

@@ -1,6 +1,8 @@
 module Liquid
   module Utils
     def self.slice_collection(collection, from, to)
+      return collection.load_slice(from, to) if collection.is_a?(ReversableRange)
+
       if (from != 0 || !to.nil?) && collection.respond_to?(:load_slice)
         collection.load_slice(from, to)
       else

lib/liquid/variable.rb

@@ -95,16 +95,17 @@ module Liquid
 
     def parse_filter_expressions(filter_name, unparsed_args)
       filter_args = []
-      keyword_args = {}
+      keyword_args = nil
       unparsed_args.each do |a|
         if matches = a.match(JustTagAttributes)
+          keyword_args ||= {}
           keyword_args[matches[1]] = Expression.parse(matches[2])
         else
           filter_args << Expression.parse(a)
         end
       end
       result = [filter_name, filter_args]
-      result << keyword_args unless keyword_args.empty?
+      result << keyword_args if keyword_args
       result
     end
 

lib/liquid/version.rb

@@ -1,5 +1,5 @@
 # encoding: utf-8
 
 module Liquid
-  VERSION = "4.0.2".freeze
+  VERSION = "4.0.3".freeze
 end

performance/memory_profile.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+require 'benchmark/ips'
+require 'memory_profiler'
+require_relative 'theme_runner'
+
+def profile(phase, &block)
+  puts
+  puts "#{phase}:"
+  puts
+
+  report = MemoryProfiler.report(&block)
+
+  report.pretty_print(
+    color_output: true,
+    scale_bytes: true,
+    detailed_report: true
+  )
+end
+
+Liquid::Template.error_mode = ARGV.first.to_sym if ARGV.first
+
+profiler = ThemeRunner.new
+
+profile("Parsing") { profiler.compile }
+profile("Rendering") { profiler.render }

test/integration/tags/for_tag_test.rb

@@ -36,6 +36,10 @@ HERE
     assert_template_result('321', '{%for item in array reversed %}{{item}}{%endfor%}', assigns)
   end
 
+  def test_for_range_reversed
+    assert_template_result('321', '{%for item in (1..3) reversed %}{{item}}{%endfor%}', {})
+  end
+
   def test_for_with_range
     assert_template_result(' 1  2  3 ', '{%for item in (1..3) %} {{item}} {%endfor%}')
 
@@ -103,6 +107,34 @@ HERE
     assert_template_result('3456', '{%for i in array limit: 4 offset: 2 %}{{ i }}{%endfor%}', assigns)
   end
 
+  def test_limiting_with_invalid_limit
+    assigns = { 'array' => [1, 2, 3, 4, 5, 6, 7, 8, 9, 0] }
+    template = <<-MKUP
+      {% for i in array limit: true offset: 1 %}
+        {{ i }}
+      {% endfor %}
+    MKUP
+
+    exception = assert_raises(Liquid::ArgumentError) do
+      Template.parse(template).render!(assigns)
+    end
+    assert_equal("Liquid error: invalid integer", exception.message)
+  end
+
+  def test_limiting_with_invalid_offset
+    assigns = { 'array' => [1, 2, 3, 4, 5, 6, 7, 8, 9, 0] }
+    template = <<-MKUP
+      {% for i in array limit: 1 offset: true %}
+        {{ i }}
+      {% endfor %}
+    MKUP
+
+    exception = assert_raises(Liquid::ArgumentError) do
+      Template.parse(template).render!(assigns)
+    end
+    assert_equal("Liquid error: invalid integer", exception.message)
+  end
+
   def test_dynamic_variable_limiting
     assigns = { 'array' => [1, 2, 3, 4, 5, 6, 7, 8, 9, 0] }
     assigns['limit'] = 2

test/integration/tags/include_tag_test.rb

@@ -30,6 +30,9 @@ class TestFileSystem
     when 'assignments'
       "{% assign foo = 'bar' %}"
 
+    when 'break'
+      "{% break %}"
+
     else
       template_path
     end
@@ -242,4 +245,9 @@ class IncludeTagTest < Minitest::Test
 
     assert_equal [], template.errors
   end
+
+  def test_break_through_include
+    assert_template_result "1", "{% for i in (1..3) %}{{ i }}{% break %}{{ i }}{% endfor %}"
+    assert_template_result "1", "{% for i in (1..3) %}{{ i }}{% include 'break' %}{{ i }}{% endfor %}"
+  end
 end # IncludeTagTest

test/integration/template_test.rb

@@ -139,6 +139,16 @@ class TemplateTest < Minitest::Test
     refute_nil t.resource_limits.assign_score
   end
 
+  def test_resource_limits_assign_score_counts_bytes_not_characters
+    t = Template.parse("{% assign foo = 'すごい' %}")
+    t.render
+    assert_equal 9, t.resource_limits.assign_score
+
+    t = Template.parse("{% capture foo %}すごい{% endcapture %}")
+    t.render
+    assert_equal 9, t.resource_limits.assign_score
+  end
+
   def test_resource_limits_assign_score_nested
     t = Template.parse("{% assign foo = 'aaaa' | reverse %}")
 
@@ -187,6 +197,14 @@ class TemplateTest < Minitest::Test
     assert_equal "ababab", t.render
   end
 
+  def test_render_length_uses_number_of_bytes_not_characters
+    t = Template.parse("{% if true %}すごい{% endif %}")
+    t.resource_limits.render_length_limit = 10
+    assert_equal "Liquid error: Memory limits exceeded", t.render
+    t.resource_limits.render_length_limit = 18
+    assert_equal "すごい", t.render
+  end
+
   def test_default_resource_limits_unaffected_by_render_with_context
     context = Context.new
     t = Template.parse("{% for a in (1..100) %} {% assign foo = 1 %} {% endfor %}")

test/unit/context_unit_test.rb

@@ -349,9 +349,9 @@ class ContextUnitTest < Minitest::Test
 
   def test_ranges
     @context.merge("test" => '5')
-    assert_equal (1..5), @context['(1..5)']
+    assert_equal ReversableRange.new(1, 5), @context['(1..5)']
-    assert_equal (1..5), @context['(1..test)']
+    assert_equal ReversableRange.new(1, 5), @context['(1..test)']
-    assert_equal (5..5), @context['(test..test)']
+    assert_equal ReversableRange.new(5, 5), @context['(test..test)']
   end
 
   def test_cents_through_drop_nestedly

test/unit/reversable_range_unit_test.rb

@@ -0,0 +1,116 @@
+require 'test_helper'
+
+class ReversableRangeTest < Minitest::Test
+  include Liquid
+
+  def test_each_iterates_through_items_in_the_range
+    actual_items = []
+    ReversableRange.new(1, 10).each { |item| actual_items << item }
+
+    expected_items = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+    assert_equal expected_items, actual_items
+  end
+
+  def test_implements_enumerable
+    actual_items = ReversableRange.new(1, 10).select(&:even?)
+
+    expected_items = [2, 4, 6, 8, 10]
+    assert_equal expected_items, actual_items
+  end
+
+  def test_is_not_empty_max_greater_than_min
+    range = ReversableRange.new(9, 10)
+
+    refute_predicate range, :empty?
+  end
+
+  def test_is_not_empty_max_equal_to_min
+    range = ReversableRange.new(10, 10)
+
+    refute_predicate range, :empty?
+  end
+
+  def test_is_empty_if_not_reversed_and_max_less_than_min
+    range = ReversableRange.new(10, 9)
+
+    assert_predicate range, :empty?
+  end
+
+  def test_ranges_with_the_same_max_and_min_have_one_element
+    actual_items = ReversableRange.new(1337, 1337).to_a
+    expected_items = [1337]
+    assert_equal expected_items, actual_items
+  end
+
+  def test_load_slice_returns_a_sub_range
+    actual_items = ReversableRange.new(1, 10).load_slice(5, 8).to_a
+
+    expected_items = [5, 6, 7, 8]
+    assert_equal expected_items, actual_items
+  end
+
+  def test_load_slice_returns_a_reversed_sub_range_if_reversed
+    range = ReversableRange.new(1, 10)
+    range.reverse!
+    actual_items = range.load_slice(5, 8).to_a
+
+    expected_items = [8, 7, 6, 5]
+    assert_equal expected_items, actual_items
+  end
+
+  def test_is_equal_to_other_if_also_a_reversable_range_and_has_same_properties
+    one = ReversableRange.new(1, 10)
+    one.reverse!
+
+    two = ReversableRange.new(1, 10)
+    two.reverse!
+
+    assert_equal one, two
+  end
+
+  def test_is_not_equal_to_a_non_reversable_range
+    range = ReversableRange.new(1, 10)
+    range.reverse!
+
+    refute_equal range, :something_else
+  end
+
+  def test_is_not_equal_if_ranges_have_different_mins
+    one = ReversableRange.new(1, 10)
+    two = ReversableRange.new(2, 10)
+
+    refute_equal one, two
+  end
+
+  def test_is_not_equal_if_ranges_have_different_maxes
+    one = ReversableRange.new(1, 10)
+    two = ReversableRange.new(1, 11)
+
+    refute_equal one, two
+  end
+
+  def test_is_not_equal_if_only_one_is_reversed
+    one = ReversableRange.new(1, 10)
+
+    two = ReversableRange.new(1, 10)
+    two.reverse!
+
+    refute_equal one, two
+  end
+
+  def test_to_s_mirrors_rubys_range_syntax
+    range = ReversableRange.new(1, 10)
+    assert_equal '1..10', range.to_s
+  end
+
+  def test_to_s_reverses_when_reversed
+    range = ReversableRange.new(1, 10)
+    range.reverse!
+    assert_equal '10..1', range.to_s
+  end
+
+  def test_size
+    range = ReversableRange.new(1, 10)
+    assert_equal 10, range.size
+  end
+end