Adds unit test for bridge implementations:
- Custom functions must be in protected or private scope
- getName() must return a valid string (non-empty)
- getURI() must return a valid URI
- Each bridge must define constants for NAME, URI, DESCRIPTION and
MAINTAINER. CACHE_TIMEOUT and PARAMETERS are optional.
The unit test is written for PHPUnit 6.x and will automatically be
tested by Travis-CI for PHP 7.0 (see .travis.yml).
Remarks:
Unit tests for bridge data were scrapped in #378 for complexity
reasons (tests would have to be maintained for each bridge). This
unit test, however, is written for testing all bridges without
taking specific implementation details into account.
