the test case seems to be for a different kata

From Ruby 3.0, RSpec is used under the hood.

See https://rspec.info/

Defaults to the global describe for backwards compatibility, but RSpec.desribe works as well.

describe "Example" do
it "should return the sum" do
expect(add(1, 1)).to eq(2)
# The following is still supported, but new tests should now use them.
# Test.assert_equals(add(1, 1), 2)
end
end