There were 4 errors:

1) phpbb_template_template_includecss_test::test_includecss_compilation with data set #0 (array(1), '<link href="tests/template/templates/child_only.css?assets_version=1" rel="stylesheet" type="text/css" media="screen, projection" />')

Argument 5 passed to phpbb\template\twig\twig::__construct() must be an instance of phpbb\template\twig\environment, instance of phpbb_mock_extension_manager given, called in /home/travis/build/phpbb/phpbb/tests/template/template_includecss_test.php on line 52 and defined

/home/travis/build/phpbb/phpbb/phpBB/phpbb/template/twig/twig.php:86

/home/travis/build/phpbb/phpbb/tests/template/template_includecss_test.php:52

/home/travis/build/phpbb/phpbb/tests/template/template_test_case.php:108

2) phpbb_template_template_includecss_test::test_includecss_compilation with data set #1 (array(2), '<link href="tests/template/parent_templates/parent_only.css?assets_version=1" rel="stylesheet" type="text/css" media="screen, projection" />')

Argument 5 passed to phpbb\template\twig\twig::__construct() must be an instance of phpbb\template\twig\environment, instance of phpbb_mock_extension_manager given, called in /home/travis/build/phpbb/phpbb/tests/template/template_includecss_test.php on line 52 and defined

/home/travis/build/phpbb/phpbb/phpBB/phpbb/template/twig/twig.php:86

/home/travis/build/phpbb/phpbb/tests/template/template_includecss_test.php:52

/home/travis/build/phpbb/phpbb/tests/template/template_test_case.php:108

3) phpbb_template_template_includecss_test::test_includecss_compilation with data set #2 (array(3), '<link href="/home/travis/build/phpbb/phpbb/tests/template/ext/include/css/styles/all/theme/test.css?assets_version=1" rel="stylesheet" type="text/css" media="screen, projection" />')

Argument 5 passed to phpbb\template\twig\twig::__construct() must be an instance of phpbb\template\twig\environment, instance of phpbb_mock_extension_manager given, called in /home/travis/build/phpbb/phpbb/tests/template/template_includecss_test.php on line 52 and defined

/home/travis/build/phpbb/phpbb/phpBB/phpbb/template/twig/twig.php:86

/home/travis/build/phpbb/phpbb/tests/template/template_includecss_test.php:52

/home/travis/build/phpbb/phpbb/tests/template/template_test_case.php:108

4) phpbb_template_template_includecss_test::test_includecss_compilation with data set #3 (array(4), '<link href="/home/travis/build/phpbb/phpbb/tests/template/ext/include/css/styles/all/theme/child_only.css?assets_version=1" rel="stylesheet" type="text/css" media="screen, projection" />')

Argument 5 passed to phpbb\template\twig\twig::__construct() must be an instance of phpbb\template\twig\environment, instance of phpbb_mock_extension_manager given, called in /home/travis/build/phpbb/phpbb/tests/template/template_includecss_test.php on line 52 and defined

/home/travis/build/phpbb/phpbb/phpBB/phpbb/template/twig/twig.php:86

/home/travis/build/phpbb/phpbb/tests/template/template_includecss_test.php:52

/home/travis/build/phpbb/phpbb/tests/template/template_test_case.php:108