Wat is this? (Ruby 1.9.3p327)

foo.rb

require 'minitest/autorun'

class FooTest < MiniTest::Unit::TestCase
  def test_foo
    assert_equal('0x0', '0x1')
  end
end

# Running tests:

# F

# Finished tests in 0.022110s, 45.2284 tests/s, 45.2284 assertions/s.

#   1) Failure:
# test_foo(FooTest) [foo.rb:4]:
# No visible difference.
# You should look at your implementation of String#==.
# "0xXXXXXX"

# 1 tests, 1 assertions, 1 failures, 0 errors, 0 skips