foo.rb

require 'rspec'
require 'rspec/autorun'

module Foo
end

RSpec.describe Foo do
 it "tests" do
  expect(subject.class).to eq(Foo)
 end
end

output

Foo
  tests (FAILED - 1)

Failures:

  1) Foo tests
     Failure/Error: expect(subject.class).to eq(Foo)

       expected: Foo
            got: Module

       (compared using ==)

       Diff:
       @@ -1,2 +1,2 @@
       -Foo
       +Module

     # ./foo.rb:9:in `block (2 levels) in <top (required)>'

Finished in 0.00131 seconds
1 example, 1 failure

Failed examples:

rspec ./foo.rb:8 # Foo tests