add builder runner spec

spec/planaria/generator/builder/runner_spec.rb

@@ -0,0 +1,20 @@
+require File.expand_path(File.join('../../../', 'spec_helper'), File.dirname(__FILE__))
+
+RSpec.describe Planaria::Generator::Builder::Runner do
+  let(:project) { "project" }
+  before { Planaria::Generator::Initializer::Executer.new(project).run }
+  after { FileUtils.rm_rf "#{APP_ROOT}/#{project}" }
+
+  describe "#run" do
+    let(:message) do
+      <<-EOS
+Generate #{project}/base.html
+      EOS
+    end
+
+    it do
+      expect { described_class.new(project).run }.to output(message).to_stdout
+      expect(File.exist?("#{APP_ROOT}/#{project}/base.html")).to be_truthy
+    end
+  end
+end