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Testing Error Handling Integration in Shopify/Liquid

This integration test suite validates error handling functionality in the Liquid templating engine, focusing on syntax errors, runtime errors, and error message formatting. It ensures proper error reporting with line numbers and template context.

Test Coverage Overview

The test suite provides comprehensive coverage of error handling scenarios in Liquid templates.

Key areas tested include:

Line number reporting in error messages
Various error types (StandardError, SyntaxError, ArgumentError)
Template parsing errors
Nested block error handling
Exception propagation and rendering

Implementation Analysis

The testing approach uses Minitest framework with systematic verification of error scenarios. It employs both strict and lax error modes to test different handling behaviors.

Key patterns include:

Template parsing with line number tracking
Custom error renderers and environments
Mock file systems for testing included templates
Error message formatting validation

Technical Details

Testing tools and configuration:

Minitest as the testing framework
Custom ErrorDrop class for error simulation
TestFileSystem mock for template inclusion tests
Environment configurations for different error modes
Line number tracking enabled/disabled testing

Best Practices Demonstrated

The test suite exemplifies robust error handling testing practices.

Notable practices include:

Comprehensive edge case coverage
Isolated test cases for specific error types
Clear error message validation
Template context preservation
Proper error propagation testing

shopify/liquid

test/integration/error_handling_test.rb

            
# frozen_string_literal: true

require 'test_helper'

class ErrorHandlingTest < Minitest::Test
  include Liquid

  def test_templates_parsed_with_line_numbers_renders_them_in_errors
    template = <<-LIQUID
      Hello,

      {{ errors.standard_error }} will raise a standard error.

      Bla bla test.

      {{ errors.syntax_error }} will raise a syntax error.

      This is an argument error: {{ errors.argument_error }}

      Bla.
    LIQUID

    expected = <<-TEXT
      Hello,

      Liquid error (line 3): standard error will raise a standard error.

      Bla bla test.

      Liquid syntax error (line 7): syntax error will raise a syntax error.

      This is an argument error: Liquid error (line 9): argument error

      Bla.
    TEXT

    output = Liquid::Template.parse(template, line_numbers: true).render('errors' => ErrorDrop.new)
    assert_equal(expected, output)
  end

  def test_standard_error
    template = Liquid::Template.parse(' {{ errors.standard_error }} ')
    assert_equal(' Liquid error: standard error ', template.render('errors' => ErrorDrop.new))

    assert_equal(1, template.errors.size)
    assert_equal(StandardError, template.errors.first.class)
  end

  def test_syntax
    template = Liquid::Template.parse(' {{ errors.syntax_error }} ')
    assert_equal(' Liquid syntax error: syntax error ', template.render('errors' => ErrorDrop.new))

    assert_equal(1, template.errors.size)
    assert_equal(SyntaxError, template.errors.first.class)
  end

  def test_argument
    template = Liquid::Template.parse(' {{ errors.argument_error }} ')
    assert_equal(' Liquid error: argument error ', template.render('errors' => ErrorDrop.new))

    assert_equal(1, template.errors.size)
    assert_equal(ArgumentError, template.errors.first.class)
  end

  def test_missing_endtag_parse_time_error
    assert_match_syntax_error(/: 'for' tag was never closed\z/, ' {% for a in b %} ... ')
  end

  def test_unrecognized_operator
    with_error_mode(:strict) do
      assert_raises(SyntaxError) do
        Liquid::Template.parse(' {% if 1 =! 2 %}ok{% endif %} ')
      end
    end
  end

  def test_lax_unrecognized_operator
    template = Liquid::Template.parse(' {% if 1 =! 2 %}ok{% endif %} ', error_mode: :lax)
    assert_equal(' Liquid error: Unknown operator =! ', template.render)
    assert_equal(1, template.errors.size)
    assert_equal(Liquid::ArgumentError, template.errors.first.class)
  end

  def test_with_line_numbers_adds_numbers_to_parser_errors
    source = <<~LIQUID
      foobar

      {% "cat" | foobar %}

      bla
    LIQUID
    assert_match_syntax_error(/Liquid syntax error \(line 3\)/, source)
  end

  def test_with_line_numbers_adds_numbers_to_parser_errors_with_whitespace_trim
    source = <<~LIQUID
      foobar

      {%- "cat" | foobar -%}

      bla
    LIQUID

    assert_match_syntax_error(/Liquid syntax error \(line 3\)/, source)
  end

  def test_parsing_warn_with_line_numbers_adds_numbers_to_lexer_errors
    template = Liquid::Template.parse(
      '
        foobar

        {% if 1 =! 2 %}ok{% endif %}

        bla
            ',
      error_mode: :warn,
      line_numbers: true,
    )

    assert_equal(
      ['Liquid syntax error (line 4): Unexpected character = in "1 =! 2"'],
      template.warnings.map(&:message),
    )
  end

  def test_parsing_strict_with_line_numbers_adds_numbers_to_lexer_errors
    err = assert_raises(SyntaxError) do
      Liquid::Template.parse(
        '
          foobar

          {% if 1 =! 2 %}ok{% endif %}

          bla
                ',
        error_mode: :strict,
        line_numbers: true,
      )
    end

    assert_equal('Liquid syntax error (line 4): Unexpected character = in "1 =! 2"', err.message)
  end

  def test_syntax_errors_in_nested_blocks_have_correct_line_number
    source = <<~LIQUID
      foobar

      {% if 1 != 2 %}
        {% foo %}
      {% endif %}

      bla
    LIQUID

    assert_match_syntax_error("Liquid syntax error (line 4): Unknown tag 'foo'", source)
  end

  def test_strict_error_messages
    err = assert_raises(SyntaxError) do
      Liquid::Template.parse(' {% if 1 =! 2 %}ok{% endif %} ', error_mode: :strict)
    end
    assert_equal('Liquid syntax error: Unexpected character = in "1 =! 2"', err.message)

    err = assert_raises(SyntaxError) do
      Liquid::Template.parse('{{%%%}}', error_mode: :strict)
    end
    assert_equal('Liquid syntax error: Unexpected character % in "{{%%%}}"', err.message)
  end

  def test_warnings
    template = Liquid::Template.parse('{% if ~~~ %}{{%%%}}{% else %}{{ hello. }}{% endif %}', error_mode: :warn)
    assert_equal(3, template.warnings.size)
    assert_equal('Unexpected character ~ in "~~~"', template.warnings[0].to_s(false))
    assert_equal('Unexpected character % in "{{%%%}}"', template.warnings[1].to_s(false))
    assert_equal('Expected id but found end_of_string in "{{ hello. }}"', template.warnings[2].to_s(false))
    assert_equal('', template.render)
  end

  def test_warning_line_numbers
    template = Liquid::Template.parse("{% if ~~~ %}\n{{%%%}}{% else %}\n{{ hello. }}{% endif %}", error_mode: :warn, line_numbers: true)
    assert_equal('Liquid syntax error (line 1): Unexpected character ~ in "~~~"', template.warnings[0].message)
    assert_equal('Liquid syntax error (line 2): Unexpected character % in "{{%%%}}"', template.warnings[1].message)
    assert_equal('Liquid syntax error (line 3): Expected id but found end_of_string in "{{ hello. }}"', template.warnings[2].message)
    assert_equal(3, template.warnings.size)
    assert_equal([1, 2, 3], template.warnings.map(&:line_number))
  end

  # Liquid should not catch Exceptions that are not subclasses of StandardError, like Interrupt and NoMemoryError
  def test_exceptions_propagate
    assert_raises(Exception) do
      template = Liquid::Template.parse('{{ errors.exception }}')
      template.render('errors' => ErrorDrop.new)
    end
  end

  def test_default_exception_renderer_with_internal_error
    template = Liquid::Template.parse('This is a runtime error: {{ errors.runtime_error }}', line_numbers: true)

    output = template.render('errors' => ErrorDrop.new)

    assert_equal('This is a runtime error: Liquid error (line 1): internal', output)
    assert_equal([Liquid::InternalError], template.errors.map(&:class))
  end

  def test_setting_default_exception_renderer
    exceptions = []
    default_exception_renderer = ->(e) {
      exceptions << e
      ''
    }

    env = Liquid::Environment.build(exception_renderer: default_exception_renderer)
    template = Liquid::Template.parse('This is a runtime error: {{ errors.argument_error }}', environment: env)

    output = template.render('errors' => ErrorDrop.new)

    assert_equal('This is a runtime error: ', output)
    assert_equal([Liquid::ArgumentError], template.errors.map(&:class))
  end

  def test_setting_exception_renderer_on_environment
    exceptions = []
    exception_renderer = ->(e) do
      exceptions << e
      ''
    end

    environment = Liquid::Environment.build(exception_renderer: exception_renderer)
    template = Liquid::Template.parse('This is a runtime error: {{ errors.argument_error }}', environment: environment)
    output = template.render('errors' => ErrorDrop.new)

    assert_equal('This is a runtime error: ', output)
    assert_equal([Liquid::ArgumentError], template.errors.map(&:class))
  end

  def test_exception_renderer_exposing_non_liquid_error
    template   = Liquid::Template.parse('This is a runtime error: {{ errors.runtime_error }}', line_numbers: true)
    exceptions = []
    handler    = ->(e) {
      exceptions << e
      e.cause
    }

    output = template.render({ 'errors' => ErrorDrop.new }, exception_renderer: handler)

    assert_equal('This is a runtime error: runtime error', output)
    assert_equal([Liquid::InternalError], exceptions.map(&:class))
    assert_equal(exceptions, template.errors)
    assert_equal('#<RuntimeError: runtime error>', exceptions.first.cause.inspect)
  end

  class TestFileSystem
    def read_template_file(_template_path)
      "{{ errors.argument_error }}"
    end
  end

  def test_included_template_name_with_line_numbers
    environment = Liquid::Environment.build(file_system: TestFileSystem.new)
    template = Liquid::Template.parse("Argument error:\n{% include 'product' %}", line_numbers: true, environment: environment)
    page     = template.render('errors' => ErrorDrop.new)

    assert_equal("Argument error:\nLiquid error (product line 1): argument error", page)
    assert_equal("product", template.errors.first.template_name)
  end

  def test_bug_compatible_silencing_of_errors_in_blank_nodes
    output = Liquid::Template.parse("{% assign x = 0 %}{% if 1 < '2' %}not blank{% assign x = 3 %}{% endif %}{{ x }}").render
    assert_equal("Liquid error: comparison of Integer with String failed0", output)

    output = Liquid::Template.parse("{% assign x = 0 %}{% if 1 < '2' %}{% assign x = 3 %}{% endif %}{{ x }}").render
    assert_equal("0", output)
  end

  def test_syntax_error_is_raised_with_template_name
    file_system = StubFileSystem.new("snippet" => "1\n2\n{{ 1")

    context = Liquid::Context.build(
      registers: { file_system: file_system },
    )

    template = Template.parse(
      '{% render "snippet" %}',
      line_numbers: true,
    )
    template.name = "template/index"

    assert_equal(
      "Liquid syntax error (snippet line 3): Variable '{{' was not properly terminated with regexp: /\\}\\}/",
      template.render(context),
    )
  end

  def test_syntax_error_is_raised_with_template_name_from_template_factory
    file_system = StubFileSystem.new("snippet" => "1\n2\n{{ 1")

    context = Liquid::Context.build(
      registers: {
        file_system: file_system,
        template_factory: StubTemplateFactory.new,
      },
    )

    template = Template.parse(
      '{% render "snippet" %}',
      line_numbers: true,
    )
    template.name = "template/index"

    assert_equal(
      "Liquid syntax error (some/path/snippet line 3): Variable '{{' was not properly terminated with regexp: /\\}\\}/",
      template.render(context),
    )
  end

  def test_error_is_raised_during_parse_with_template_name
    depth = Liquid::Block::MAX_DEPTH + 1
    code = "{% if true %}" * depth + "rendered" + "{% endif %}" * depth

    template = Template.parse("{% render 'snippet' %}", line_numbers: true)

    context = Liquid::Context.build(
      registers: {
        file_system: StubFileSystem.new("snippet" => code),
        template_factory: StubTemplateFactory.new,
      },
    )

    assert_equal("Liquid error (some/path/snippet line 1): Nesting too deep", template.render(context))
  end

  def test_internal_error_is_raised_with_template_name
    template = Template.new
    template.parse(
      "{% render 'snippet' %}",
      line_numbers: true,
    )
    template.name = "template/index"

    context = Liquid::Context.build(
      registers: {
        file_system: StubFileSystem.new({}),
      },
    )

    assert_equal(
      "Liquid error (template/index line 1): internal",
      template.render(context),
    )
  end
end