Use shoulda_matchers

In recent versions of shoulda-matchers (at least as of v2.7.0), you can do:

expect(subject).to validate_inclusion_of(:active).in_array(%w[Y N])

This tests that the array of acceptable values in the validation exactly matches this spec.

In earlier versions, >= v1.4 , shoulda_matchers supports this syntax:

it {should ensure_inclusion_of(:active).in_array(%w[Y N]) }