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Unit tests ensure the quality and correctness of your code, especially when doing large code refactorings, and prevent regressions. Zulip uses node to unit test its 150+ JavaScript files. Help add test coverage to Zulip!

Instructions for this task are at https://github.com/zulip/zulip-gci/blob/master/tasks/2017/node-coverage.md

For this task, you will be testing the file stream_data.js. The functions that require coverage are:

• exports.remove_subscriber
• exports.user_is_subscribed