add tests

lib/github_changelog_generator/generator/generator.rb

@@ -18,13 +18,9 @@ module GitHubChangelogGenerator
     #   generator = GitHubChangelogGenerator::Generator.new
     #   content = generator.compound_changelog
     def initialize(options = nil)
-      @options = options
+      @options = options || {}
 
       @fetcher = GitHubChangelogGenerator::Fetcher.new @options
-
-      fetch_and_filter_tags
-
-      fetch_issues_and_pr
     end
 
     def fetch_issues_and_pr

lib/github_changelog_generator/generator/generator_generation.rb

@@ -4,6 +4,9 @@ module GitHubChangelogGenerator
     #
     # @return [String] Generated change log file
     def compound_changelog
+      fetch_and_filter_tags
+      fetch_issues_and_pr
+
       log = "# Change Log\n\n"
 
       if @options[:unreleased_only]