how to test ruby inheritance with rspec - ruby

Question

I am trying to test logic that runs during class inheritance, but have run into an issue when running multiple assertions.
i first tried...
describe 'self.inherited' do
before do
class Foo
def self.inherited klass; end
end
Foo.stub(:inherited)
class Bar < Foo; end
end
it 'should call self.inherited' do
# this fails if it doesn't run first
expect(Foo).to have_received(:inherited).with Bar
end
it 'should do something else' do
expect(true).to eq true
end
end
but this fails because the Bar class has already been loaded, and therefore does not call inherited a 2nd time. If the assertion doesn't run first... it fails.
So then i tried something like...
describe 'self.inherited once' do
before do
class Foo
def self.inherited klass; end
end
Foo.stub(:inherited)
class Bar < Foo; end
end
it 'should call self.inherited' do
#tested ||= false
unless #tested
expect(Foo).to have_receive(:inherited).with Bar
#tested = true
end
end
it 'should do something else' do
expect(true).to eq true
end
end
because #tested doesn't persist from test to test, the test doesn't just run once.
anyone have any clever ways to accomplish this? This is a contrived example and i dont actually need to test ruby itself ;)

Answer 1

Here's an easy way to test for class inheritance with RSpec:
Given
class A < B; end
a much simpler way to test inheritance with RSpec would be:
describe A do
it { expect(described_class).to be < B }
end

Answer 2

For something like this
class Child < Parent; end
I usually do:
it 'should inherit behavior from Parent' do
expect(Child.superclass).to eq(Parent)
end

Answer 3

For some reason, I did not manage the solution from David Posey to work (I guess I did something wrong. Feel free to provide a solution in the comments). In case someone out there have the same problem, this works too:
describe A
it { expect(described_class.superclass).to be B }
end

Answer 4

Make your class definition for testing inheritance run during the test:
describe 'self.inherited' do
before do
class Foo
def self.inherited klass; end
end
# For testing other properties of subclasses
class Baz < Foo; end
end
it 'should call self.inherited' do
Foo.stub(:inherited)
class Bar < Foo; end
expect(Foo).to have_received(:inherited).with Bar
end
it 'should do something else' do
expect(true).to eq true
end
end

Answer 5

Another way:
class Foo; end
class Bar < Foo; end
class Baz; end
RSpec.describe do
it 'is inherited' do
expect(Bar < Foo).to eq true
end
it 'is not inherited' do
expect(Baz < Foo).not_to eq true
end
end