refactor and add tests

Author: bishosilwal

lib/imagekitio/file.rb

@@ -45,7 +45,6 @@ def upload(file, file_name, options)
     end
 
     def update_details(file_id, options)
-      # Update file detail by file_id and options
       unless options.fetch(:tags, []).is_a?(Array)
         raise ArgumentError, constants.UPDATE_DATA_TAGS_INVALID
       end
@@ -226,13 +225,16 @@ def create_custom_metadata(name, label, schema)
       @req_obj.request('post', url, @req_obj.create_headers, payload)
     end
 
-    def get_custom_metadata(options)
+    def get_custom_metadata(options = {})
       url = "#{constants.API_BASE_URL}/customMetadataFields"
       payload = request_formatter(options)
       @req_obj.request('get', url, @req_obj.create_headers, payload)
     end
 
     def update_custom_metadata(id, label, schema)
+      if id == '' || id.nil?
+        raise ArgumentError, 'id is required'
+      end
       url = "#{constants.API_BASE_URL}/customMetadataFields/#{id}"
       payload = {}
       payload = payload.merge({ 'label': label }) unless label.nil?
@@ -241,6 +243,9 @@ def update_custom_metadata(id, label, schema)
     end
 
     def delete_custom_metadata(id)
+      if id == '' || id.nil?
+        raise ArgumentError, 'id is required'
+      end
       url = "#{constants.API_BASE_URL}/customMetadataFields/#{id}"
       @req_obj.request('delete', url, @req_obj.create_headers)
     end