Add due-tag option and tests

lib/github_changelog_generator/generator/generator_tags.rb

@@ -91,6 +91,27 @@ module GitHubChangelogGenerator
       filtered_tags
     end
 
+    # @param [Array] all_tags all tags
+    # @return [Array] filtered tags according :due_tag option
+    def filter_due_tag(all_tags)
+      filtered_tags = all_tags
+      tag = @options[:due_tag]
+      if tag
+        if (all_tags.count > 0) && (all_tags.map(&:name).include? tag)
+          idx = all_tags.index { |t| t.name == tag }
+          last_index = all_tags.count - 1
+          if idx > 0 && idx < last_index
+            filtered_tags = all_tags[idx + 1..last_index]
+          else
+            filtered_tags = []
+          end
+        else
+          Helper.log.warn "Warning: can't find tag #{tag}, specified with --due-tag option."
+        end
+      end
+      filtered_tags
+    end
+
     # @param [Array] all_tags all tags
     # @return [Array] filtered tags according :between_tags option
     def filter_between_tags(all_tags)