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Testing JavaScript Evaluation Methods in Capybara Framework

This test suite evaluates Capybara’s JavaScript evaluation capabilities through the #evaluate_script method. It verifies script execution, argument passing, and element manipulation in web applications using Capybara’s testing framework.

Test Coverage Overview

The test suite comprehensively covers the #evaluate_script functionality in Capybara, focusing on JavaScript execution scenarios.

Basic script evaluation and return value verification
Whitespace handling in scripts
Argument passing to JavaScript functions
DOM element manipulation and interaction
Support for complex multi-statement scripts

Implementation Analysis

The testing approach employs RSpec-style syntax with Capybara’s session object to validate JavaScript functionality. Tests utilize a combination of direct script evaluation and DOM manipulation patterns, leveraging Capybara’s ability to interact with JavaScript-enabled pages.

Uses RSpec expect syntax for assertions
Implements before-visit patterns for page setup
Employs element finding and manipulation techniques

Technical Details

Requires JavaScript-capable driver (:js requirement)
Uses ES arguments feature for advanced testing
Implements IIFE pattern for complex JavaScript execution
Leverages Capybara::Node::Element for DOM interaction
Utilizes CSS selectors for element identification

Best Practices Demonstrated

The test suite exemplifies robust testing practices by covering various edge cases and usage patterns.

Isolated test cases for specific functionality
Clear test descriptions and expectations
Progressive complexity in test scenarios
Proper setup and teardown patterns
Comprehensive feature validation

teamcapybara/capybara

lib/capybara/spec/session/evaluate_script_spec.rb

            
# frozen_string_literal: true

Capybara::SpecHelper.spec '#evaluate_script', requires: [:js] do
  it 'should evaluate the given script and return whatever it produces' do
    @session.visit('/with_js')
    expect(@session.evaluate_script('1+3')).to eq(4)
  end

  it 'should ignore leading whitespace' do
    @session.visit('/with_js')
    expect(@session.evaluate_script('
      1 + 3
    ')).to eq(4)
  end

  it 'should pass arguments to the script', requires: %i[js es_args] do
    @session.visit('/with_js')
    expect(@session).to have_css('#change')
    @session.evaluate_script("document.getElementById('change').textContent = arguments[0]", 'Doodle Funk')
    expect(@session).to have_css('#change', text: 'Doodle Funk')
  end

  it 'should support passing elements as arguments to the script', requires: %i[js es_args] do
    @session.visit('/with_js')
    el = @session.find(:css, '#change')
    @session.evaluate_script('arguments[0].textContent = arguments[1]', el, 'Doodle Funk')
    expect(@session).to have_css('#change', text: 'Doodle Funk')
  end

  it 'should support returning elements', requires: %i[js es_args] do
    @session.visit('/with_js')
    @session.find(:css, '#change') # ensure page has loaded and element is available
    el = @session.evaluate_script("document.getElementById('change')")
    expect(el).to be_instance_of(Capybara::Node::Element)
    expect(el).to eq(@session.find(:css, '#change'))
  end

  it 'should support multi statement via IIFE' do
    @session.visit('/with_js')
    @session.find(:css, '#change')
    el = @session.evaluate_script(<<~JS)
      (function(){
        var el = document.getElementById('change');
        return el;
      })()
    JS
    expect(el).to eq(@session.find(:css, '#change'))
  end
end