Testing

bundle exec rspec
bundle exec rubocop
bundle exec rake docs:check

CI runs all three on Ruby 3.2, 3.3 and 3.4.

The rules

No real network. spec_helper.rb loads WebMock, so an unstubbed request fails the spec. Stub the provider endpoints.
Never touch real configuration. Build credentials with Messengerr::Credentials.new(credentials_path:, key_path:) pointing into a Dir.mktmpdir. A bare Credentials.new would read ~/.config/messengerr.
No stray files. Pass --ledger a temp path in CLI specs so nothing is written to the working directory.
Environment variables go through with_env (spec/support/env_helper.rb), which restores them afterwards.
Specs run in random order, with partial doubles verified and monkey patching disabled.

Helpers

Integrations::Fake (spec/support/fake_integration.rb): an email integration that fails rows whose fail column is yes. Use it for wizard, sender and ledger flows.
fixtures/contacts.csv: a small list with deliberately bad rows.
For the wizard, build a Prompter over StringIO input and output, as send_command_spec.rb does. Answers are positional, so keep each script readable and commented.

What to cover

Provider code: every uncertain and definite failure, with stubbed responses. These decide whether users are warned before a retry.
Flows: declining the confirmation sends nothing, --dry-run sends nothing and writes no ledger, --resume skips exactly the right rows, Ctrl-C leaves an honest ledger.
Anything crossing layers (CLI plus a real integration) gets an end-to-end spec. A unit spec on one class once passed while every email send was broken.

Prove the spec tests the fix

After a spec passes, temporarily revert the fix (or change the behaviour it guards) and confirm the spec fails. Then restore it. A spec that stays green against the bug is not testing it. This is done by hand today; there is no mutation-testing tool in the project.

Docs check

bundle exec rake docs:check fails if docs/integrations.md no longer matches the integration registry. Fix it with bundle exec rake docs:integrations and commit.