Null object doubles

Test doubles are strict by default, raising errors when they receive messages that have not been allowed or expected. You can chain as_null_object off of double in order to make the double “loose”. For any message that has not explicitly allowed or expected, the double will return itself. It acts as a black hole null object, allowing arbitrarily deep method chains.

as_null_object allows arbitrarily deep message chains and returns itself

Given a file named “asnullobject_spec.rb” with:

RSpec.describe "as_null_object" do
  it "returns itself" do
    dbl = double("Some Collaborator").as_null_object
    expect(dbl.foo.bar.bazz).to be(dbl)
  end
end

When I run rspec as_null_object_spec.rb

Then the examples should all pass.

Individual methods can still be allowed or expected

Given a file named “asnullobject_spec.rb” with:

RSpec.describe "as_null_object" do
  it "can allow individual methods" do
    dbl = double("Some Collaborator", :foo => 3).as_null_object
    allow(dbl).to receive(:bar).and_return(4)

    expect(dbl.foo).to eq(3)
    expect(dbl.bar).to eq(4)
  end
end

When I run rspec as_null_object_spec.rb

Then the examples should all pass.