test that startSketch must have been called when play button is clicked

[vulongphan]

Fixes #1823

I have verified that this pull request:

• has no linting errors (npm run lint)
• is from a uniquely-named feature branch and has been rebased on top of the latest develop branch. (If I was asked to make more changes, I have made sure to rebase onto develop then too)
• is descriptively named and links to an issue number, i.e. Fixes #123

[release-com]

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[catarak]

Thanks for working on this! You have some extraneous changes to package.json and package-lock.json that shouldn't be in this PR.