Now that's a test list!

gist_no_css_tag_spec.rb

require "rspec"

describe "gist_no_css tag" do
  context "the pieces" do
    context "rendering code" do
      # Assume we've already successfully downloaded code
      example "gist ID, username and filename"
      example "gist ID and filename"
      example "gist ID and username"
      example "gist ID"
    end

    context "downloading gist code" do
      context "gist found" do
        context "gist has only one file" do
          example "filename specified"
          example "filename not specified"
          example "filename does not match"
        end
        context "gist has many files" do
          context "filename specified" do
            example "matches first file"
            example "matches other-than-first file"
            example "filename does not match"
          end
          example "filename not specified"
        end
      end
      example "gist not found"
      example "failure downloading gist"
    end

    context "parsing tag parameters" do
      example "all parameters specified" do
        pending
        # Remember to call the codeblock with filename, then URL
      end
      example "username not specified"
      example "filename not specified"
      example "only gist ID specified"
      context "failure cases" do
        example "no parameters"
        example "only username"
        example "only filename"
        example "username and filename"
      end
    end
  end

  context "integrating the pieces into the Liquid extension point" do
    it "should be a Liquid tag"
    it "should register itself in Liquid"

    describe "render()" do
      example "happy path"
      example "failure rendering code"
      example "failure downloading gist"
    end

    describe "initialize()" do
      example "happy path"
      example "parsing parameters fails"
    end
  end
end

test_list_as_documentation.txt

gist_no_css tag
  the pieces
    rendering code
      gist ID, username and filename (PENDING: Not yet implemented)
      gist ID and filename (PENDING: Not yet implemented)
      gist ID and username (PENDING: Not yet implemented)
      gist ID (PENDING: Not yet implemented)
    downloading gist code
      gist not found (PENDING: Not yet implemented)
      failure downloading gist (PENDING: Not yet implemented)
      gist found
        gist has only one file
          filename specified (PENDING: Not yet implemented)
          filename not specified (PENDING: Not yet implemented)
          filename does not match (PENDING: Not yet implemented)
        gist has many files
          filename not specified (PENDING: Not yet implemented)
          filename specified
            matches first file (PENDING: Not yet implemented)
            matches other-than-first file (PENDING: Not yet implemented)
            filename does not match (PENDING: Not yet implemented)
    parsing tag parameters
      all parameters specified (PENDING: No reason given)
      username not specified (PENDING: Not yet implemented)
      filename not specified (PENDING: Not yet implemented)
      only gist ID specified (PENDING: Not yet implemented)
      failure cases
        no parameters (PENDING: Not yet implemented)
        only username (PENDING: Not yet implemented)
        only filename (PENDING: Not yet implemented)
        username and filename (PENDING: Not yet implemented)
  integrating the pieces into the Liquid extension point
    should be a Liquid tag (PENDING: Not yet implemented)
    should register itself in Liquid (PENDING: Not yet implemented)
    render()
      happy path (PENDING: Not yet implemented)
      failure rendering code (PENDING: Not yet implemented)
      failure downloading gist (PENDING: Not yet implemented)
    initialize()
      happy path (PENDING: Not yet implemented)
      parsing parameters fails (PENDING: Not yet implemented)

Maybe I ought to use specify instead of context, as that words feels like it fits better. Notice that I don't use it very often. I prefer example for many special cases of a single behavior.