Testing package

[roxblnfk]

Need to write testing utilities and helpers to test Testo using Testo in tests.

src/Testing is good place for it.

In self tests we need attributes:

• ExpectTestStatus(Status)
• ExpectTestResultAttrbute(string $name) - check the attribute exists in the result
• ExpectAssertionsCount(int) - fail if there were less or more assertions

Feature and acceptance tests require a launcher helper like this.