```ruby
require "gitmethere/version"

require 'git'

module GitMeThere

  class Scenario

    # All scenarios are automatically generated as a fresh repositorywith a README.md file
    # and an initial commit on the master branch.
    #
    # If an explanation is specified, it will be included as README.md text in the first commit.
    # If no name is specified, the repository will be created with the default name: `my-scenario`.
    #
    # Example:
    #   >> scenario = GitMeThere::Scenario.new(name="my-scenario", explanation="This is my scenario")
    #
    # Arguments:
    #   name: (String)
    #   explanation: (String)
    #
    def initialize(name="my-scenario", explanation="")
      @name = name
      @g = Git.init(name)

      self.create_file(name='README.md', content=explanation)
      @g.add
      @g.commit("Initial commit")
    end

    def checkout_branch(branch)
      @g.branch(branch).checkout
    end

    def stage_changes
      @g.add
    end

    def create_file(name="my-file.md", content="")
      File.open("#{@name}/#{name}", 'w') do | f |
        f.puts content
      end
    end

    def append_to_file(name="myfile.md", content="Adding a bit more content")
      File.open("#{@name}/#{name}", 'a') do | f |
        f.puts content
      end
    end

    def commit(message)
      @g.commit(message)
    end

  end

end
```

Update Scenario to pass tests
user
```ruby
require "gitmethere/version"

require 'git'

module GitMeThere

  class Scenario

    # All scenarios are automatically generated as a fresh repositorywith a README.md file
    # and an initial commit on the master branch.
    #
    # If an explanation is specified, it will be included as README.md text in the first commit.
    # If no name is specified, the repository will be created with the default name: `my-scenario`.
    #
    # Example:
    #   >> scenario = GitMeThere::Scenario.new(name="my-scenario", explanation="This is my scenario")
    #
    # Arguments:
    #   name: (String)
    #   explanation: (String)
    #
    def initialize(name="my-scenario", explanation="")
      @name = name
      @g = Git.init(name)

      self.create_file(name='README.md', content=explanation)
      @g.add
      @g.commit("Initial commit")
    end

    def checkout_branch(branch)
      @g.branch(branch).checkout
    end

    def stage_changes
      @g.add
    end

    def create_file(name="my-file.md", content="")
      File.open("#{@name}/#{name}", 'w') do | f |
        unless content.empty?
          f.puts content
        end
      end
    end

    def append_to_file(name="my-file.md", content="Adding a bit more content")
      File.open("#{@name}/#{name}", 'a') do | f |
        f.puts content
      end
    end

    def commit(message)
      @g.commit(message)
    end

  end

end
```
assistant