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+# Making Changes To Standard Libraries
+
+Everything in the [lib](https://github.com/ruby/ruby/tree/master/lib) directory is mirrored from a standalone repository into the Ruby repository.
+If you'd like to make contributions to standard libraries, do so in the standalone repositories, and the
+changes will be automatically mirrored into the Ruby repository.
+
+For example, CSV lives in [a separate repository](https://github.com/ruby/csv) and is mirrored into [Ruby](https://github.com/ruby/ruby/tree/master/lib/csv).
+
+## Maintainers
+
+You can find the list of maintainers [here](https://docs.ruby-lang.org/en/master/maintainers_md.html#label-Maintainers).
+
+## Build
+
+First, install its dependencies using:
+
+```
+bundle install
+```
+
+### Libraries with C-extension
+
+If the library has a `/ext` directory, it has C files that you need to compile with:
+
+```
+bundle exec rake compile
+```
+
+## Running tests
+
+All standard libraries use [test-unit](https://github.com/test-unit/test-unit) as the test framework.
+
+To run all tests:
+
+```
+bundle exec rake test
+```
+
+To run a single test file:
+
+```
+bundle exec rake test TEST="test/test_foo.rb"
+```
+
+To run a single test case:
+
+```
+bundle exec rake test TEST="test/test_foo.rb" TESTOPS="--name=/test_mytest/"
+```