removed test base class
minor #93 removed test base class (fabpot)

This PR was merged into the 2.6.x-dev branch.

Discussion
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removed test base class

`TestCase` is an old class that was used in Symfony before Composer. Anyway, it was not used consistently used in the code and the error could never occurred as PHPUnit tries to load `vendor/autoload.php` first, which ensure that Monolog exists when running the tests.

Commits
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9987326 removed test base class