When run with the two lines relating to plugins deleted or on the jenkins CI server, the plugins test dies after test 16, having failed test 13:
jcamins@kohadev:~/kohaclone$ perl t/db_dependent/Plugins.t                                                                                                               
1..20
ok 1 - use Koha::Plugins;
ok 2 - use Koha::Plugins::Handler;
ok 3 - use Koha::Plugins::Base;
ok 4 - use Koha::Plugin::Test;
ok 5 - Test can_load
ok 6 - Test plugin class isa Koha::Plugin::Test
ok 7 - Test plugin parent class isa Koha::Plugins::Base
ok 8 - Test plugin can report
ok 9 - Test plugin can tool
ok 10 - Test plugin can configure
ok 11 - Test plugin can install
ok 12 - Test plugin can install
Use of uninitialized value in string eq at t/db_dependent/Plugins.t line 36.
not ok 13 - Test run plugin report method
#   Failed test 'Test run plugin report method'
#   at t/db_dependent/Plugins.t line 36.
ok 14 - Test $plugin->get_metadata()
ok 15 - Test $plugin->get_qualified_table_name()
ok 16 - Test $plugin->get_plugin_http_path()
Can't call method "GetPlugins" on an undefined value at t/db_dependent/Plugins.t line 44.
# Looks like you planned 20 tests but ran 16.
# Looks like you failed 1 test of 16 run.
# Looks like your test exited with 255 just after 16.