Suppose I have a pretty simple Rake task:
task :test do
system "bundle exec rspec spec"
end
I try testing it by stubbing the ::Kernel.system method call:
describe "test" do
before { allow(::Kernel).to receive(:system) }
it "runs 'bundle exec rspec spec'" do
expect(::Kernel).to receive(:system).with "bundle exec rspec spec"
Rake::Task[:test].invoke
end
end
But the method seems not to be stubbed at all. Instead, I run into the infinite cycle of iterations calling the test suite.
What's wrong with it, and howto stub system calls properly?
Note that Kernel is a module which is included into every ruby Object. And Kernel#system is an instance method (not a class method).
One solution (although discouraged by rspec maintainers) is to use "Any instance":
it "runs 'bundle exec rspec spec'" do
expect_any_instance_of(Kernel).to receive(:system).with "bundle exec rspec spec"
Rake::Task[:test].invoke
end
In order to use regular expect or allow, you will need the actual instance of the object which is receiving the message. For a Rake task this will be cumbersome (although not impossible - see this question) - they are executed in the toplevel context.
I would propose that you encapsulate your system calls into utility class methods and expect those. It would make the testing easier and you have explicit classes & instances to work with.
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