Fix assert conflicts in `test\Unit` adding `assetNotIdentical()`

- assertXX & assertNotXX should share the same code base.
- consistent API for `assetNotNull()`.
- adding missing `assetNotIdentical()`.
- typo fix: renaming `$actual` to `$result` all way long
- remove `assertRegExp()`, conflict with `assertPattern()`.
- remove `assertNotRegExp`, conflict with `assertNoPattern()`.
- remove `assertEmpty()`, conflict with `assertFalse()`.
- remove `assertNotEmpty()`, conflict with `assertTrue()`.