PHPUnit and Mockery as require-dev dependencies

Problem 1
    - Can only install one of: mockery/mockery[dev-master, 0.8.0].
    - Can only install one of: mockery/mockery[dev-master, 0.8.0].
    - samvaughton/ldt dev-master requires mockery/mockery dev-master@dev -> satisfiable by mockery/mockery[dev-master].
    - Installation request for samvaughton/ldt dev-master -> satisfiable by samvaughton/ldt[dev-master].
    - Installation request for mockery/mockery 0.8.0 -> satisfiable by mockery/mockery[0.8.0].