Fixed test file name

[Bilge]

• Fixed test file name. PHPUnit tests should end with Test verbatim. The class name already did, so the file name was updated to match. This fixes an issue where targeting the tests directory, e.g. vendor/bin/phpunit tests did not find any tests to run.
• Removed test bootstrap because it didn't do anything.
• Added final to indicate inheritance of test case is not intended.
• Changed visibility of member variable to private because class is final.
• Changed visibility of overridden setUp method to match parent.
• Changed Travis to use Composer invocation of test suite, since such a script is defined for this purpose already but not currently used. Doesn't work on PHP < 5.6.
• Fixed code coverage generation.

This is just a first pass to fix the major test issues. More to follow if this PR is accepted.

[JayBizzle]

Looks good!