generalize the argument name in tests, be more specific about when filename is in a different part of the multipart body
generalize the argument name in tests, be more specific about when filename is in a different part of the multipart body

slackapi/node-slack-sdk,slackapi/node-slack-sdk,slackapi/node-slack-sdk,slackhq/node-slack-client,slackhq/node-slack-sdk,slackapi/node-slack-sdk