tagName of element created by `lwc:component` is hard-coded to x-test

[gaurav-rk9]

tagName of element created by lwc:component should be computed based on the component name. Instead it seems to be hard-coded to x-test

for an example, see https://stackblitz.com/edit/salesforce-lwc-zoz2xspw?file=src%2Fmodules%2Fy%2Fapp%2F__tests__%2Fapp.spec.js and run npm run test:unit

[ekashida]

I think this was by design, but @jmsjtu can clarify