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Description

Building upon #615, make it so that tests can be run without specifying the directory:

# Run a single test file tests/units/test_archive.rb:
$ bin/test test_archive
...
# Run a multiple test files tests/units/test_archive.rb and tests/units/test_object.rb:
$ bin/test test_archive test_object
...
# Run all tests:
$ bin/test
...