RSpec-Mocks: instance_double consistency during credential isolation

Answer the question first

RSpec automatically clears verified doubles created in before(:each) by running its built‑in after(:each) hook. The mock registry is flushed after every example, so a double defined in before(:each) never sees state from a previous test.

When a double is created in before(:all), it lives for the entire example group. RSpec does not reset the mock registry until the group finishes, meaning the double can be reused by subsequent examples in the same group – and, if the same double is referenced in other groups that share the same before(:all) block, it can leak across unrelated examples.

Why before(:all) is risky

• Shared state is not automatically isolated between examples.
• Leaking doubles can cause false positives or hidden failures in later tests.
• Resetting the registry in one group can unexpectedly affect other groups that rely on the same shared setup.

Recommended approach to prevent leaks

1. Prefer let or before(:each) for doubles. This guarantees a fresh instance for every example and keeps the registry clean automatically.
2. If you must use before(:all) (e.g., expensive setup), add an after(:each) hook that resets the mock configuration:

   before(:all) do
     @api = instance_double('ExternalApi')
     allow(@api).to receive(:fetch).and_return(...)
   end
   
   after(:each) do
     RSpec::Mocks::Configuration.instance.reset
   end
   

3. Never reset the mock registry globally in a shared before(:all) hook. That would wipe out stubs defined in other example groups that legitimately share state.
4. Keep verify_doubles enabled. It ensures that any signature mismatch is caught during the example’s teardown.

Quick sanity check

Run a small suite that defines a double in before(:all) and observe that a later example can still call it. Then add the after(:each) reset hook and confirm the double is cleared.

Diagnostic question

Do you currently have any before(:all) blocks that create instance_double objects? If so, adding an after(:each) reset hook is the safest way to avoid leakage.