add tests for and fix #613, test toDOMElement() via mocked elements

[Connum]

Description

This fixes #613 which was caused by an if statement that could never be fulfilled, leading to Path properties not all making their way to the generated SVG output of toSVG(). It also fixes the properties being completely ignored by toDOMElement() and allows to test that function in the first place by mocking document.createElementNS().

Motivation and Context

We weren't able to test toDOMElement() in Node context before, that's why we missed that the properties were completely ignored. There was also no test case that would have caught the missing property for toSVG().

How Has This Been Tested?

npm run test

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I did npm run test and all tests passed green (including code styling checks).
• I have added tests to cover my changes.
• My change requires a change to the documentation.
• I have updated the README accordingly.
• I have read the CONTRIBUTING document.

[yne]

LGTM