fix docker build & add test for docker build

[xgui3783]

• [x] Run npm test successfully.

• [x] Run npm run mochasuccessfully.

• [x] test_screenshots generates the same test pictures in test as there were in test/reference and does not show any errors

• [x] I implemented tests for the new changes OR

• [ ] These changes do not require tests because _____

• [ ] These changes fix #__ (github issue number if applicable).

[katjaq]

Thank you so much @xgui3783 ! ⭐ 🚀 🌟