Why does ruby class comparison fail in this case statement?

Given the following rspec example, why is when Question not truthy?

require "rails_helper"
class Question
end

describe Question do
  it "confuses me" do
    klass = Question

    # this passes
    expect(klass).to eq(Question)

    # this doesn't fail (thankfully)
    fail "loudly" if klass != Question

    case klass
    when Question # this doesn't match 🤔???
      tada = "🎉"
      expect(tada).to eq("🎉")
    else
      # why?????
      fail "into confusion"
    end
  end
end

And no this isn't a course assignment lol. I ran into this at work and now I don't know what's true anymore.

side note, using string comparison works:

require "rails_helper"
class Question
end

describe Question do
  it "confuses me" do
    klass = Question

    # this passes
    expect(klass).to eq(Question)

    # this doesn't fail (thankfully)
    fail "loudly" if klass != Question

    case klass.to_s
    when Question.to_s # this doesn't match 🤔???
      tada = "🎉"
      expect(tada).to eq("🎉")
    else
      # why?????
      fail "into confusion"
    end
  end
end

another aside: using rspec was a convenient way to test this unexpected behavior. this issue isn't related to rspec.

It looks like you are mixing up classes and instances.

Normally when you use a class in a when clause inside a case statement, you are testing whether the variable is an instance of that class:

obj = Question.new # Note the 'new' here

case obj
when Question
  # obj is an instance of Question, so this will match.
  puts "matches Question"

when SomethingElse
  # instances of SomethingElse would match here.
  puts "matches Something else"
end

# => Outputs "matches Question"

In your example, you aren’t testing an instance of Question, but rather Question itself, which is a class and therefore an instance of Class:

klass = Question  # No 'new', just Question itself.

case klass
when Question
  # klass isn't an instance of Question, so this doesn't match...
  puts "matches Question"

when Class
  # klass actually is Question, which is an instance of Class,
  # so this does match.
  puts "matches Class"

end

# => Outputs "matches Class".

This works because of how Module.=== is defined (Class is a subclass of Module):

> mod === obj → true or false
>
> Case Equality—Returns true if obj is an instance of mod or an instance of one of mod’s descendants. Of limited use for modules, but can be used in case statements to classify objects by class.

With Strings, === is an alias of ==, so when clauses will match on equality.

Update: the original solution I posted worked because of the string comparison, but was implementing === on the instance and not on the class. I removed the .to_s and converted === into self.=== and now the example solution below works for me they way I expect.

Corrected Original:
I just learned that if I want to compare two classes, they both will need to implement self.===. Here's a working example:

require "rails_helper"
class Question
  def self.===(other)
    other == self
  end
end

describe Question do
  it "confuses me" do
    klass = Question

    # this passes
    expect(klass).to eq(Question)

    # this doesn't fail (thankfully)
    fail "loudly" if klass != Question

    case klass
    when Question
      tada = "🎉"
      expect(tada).to eq("🎉")
    else
      fail "fail? it'll never fail :) "
    end
  end
end

And here's the article that helped me find that answer:
https://thoughtbot.com/blog/case-equality-operator-in-ruby