Add basic functionality tests migrated from jsoup

[testmigrator]

This pull request adds a set of tests for basic functionality that have been migrated from the well-known jsoup library. These tests have been run and verified to ensure that they work properly with the htmlparser library, and are aimed at improving the overall test coverage of the library.

I hope that these tests will be helpful for testing the functionality of your library.

[testmigrator]

I kindly request the author to consider and accept the converted unit tests, which have been thoroughly compiled and verified.

[mylogin]

Thanks for the tests, I'll take them after some review