Test enhancement

[peter279k]

Changed log

• To support latest stable PHPUnit version easily, using the `PHPUnit\Framework\TestCase\ namesapce.
• Removing the --dev option because this it's deprecated.

The deprecated warning message is as follows:

You are using the deprecated option "dev". Dev packages are installed by default now.

• Using the the assertCount to assert expected count is same as result.
• Using the ::class to make class instance during assertInstance assertion.
• Removing unused namespace.
• Using the require __DIR__ . '/../vendor/autoload.php'; directly on bootstrap.php and it will load required classes automatically.