Test enhancement

[peter279k]

Changed log

• Add the .phpunit.result.cache in .gitignore because cached unit test result file should not be under the Git version control.
• Add EOF(end of file) for every file.
• Change the namespace to TwigTests and using TwigTest class for TwigTest.php file because of consistency.
• Add the autoload-dev block to define test class namespaces and this will be load the test classes automatically.
• Upgrade the PHPUnit to 8.x version because this view package requires php-7.2 at least now.
• The assertStringContains will be deprecated warning message since using the PHPUnit 8.
  Using the assertStringContains instead.
• The epxectedException comment annotation is deprecated since using the PHPUnit 8.
  Using the expectException method instead.
• To be compatible with TestCase::setUp method, it should be protected function setUp(): void.

References

• https://phpunit.de/getting-started/phpunit-8.html
• https://phpunit.readthedocs.io/en/8.2/fixtures.html#more-setup-than-teardown
• https://github.com/sebastianbergmann/phpunit/blob/8.0.0/ChangeLog-8.0.md#800---2019-02-01