[SDTEST-3871] Add runtime tags env alias

[anmarchenko]

What

Add DD_TEST_OPTIMIZATION_RUNTIME_TAGS as an alias for DD_TEST_OPTIMIZATION_RUNNER_RUNTIME_TAGS when configuring runtime tag overrides. Document the alias in the settings table and cover alias precedence in settings tests.

Why

This gives users a way to set one runtime-tags environment variable compatible with datadog-ci gem variable.

E2E testing

Run DD_TEST_OPTIMIZATION_RUNTIME_TAGS='{"os.platform":"linux","runtime.version":"3.2.0"}' ddtest plan in a repository configured for DDTest and verify the plan uses those runtime tags when fetching skippable tests.

[datadog-datadog-prod-us1]

 

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 25.00%
• Overall Coverage: 88.12% (-0.05%)

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[datadog-datadog-prod-us1]

More details

The alias implementation is correct. Viper v1.21's BindEnv with multiple env vars follows first-non-empty semantics (allowEmptyEnv defaults to false), so DD_TEST_OPTIMIZATION_RUNTIME_TAGS is used whenever DD_TEST_OPTIMIZATION_RUNNER_RUNTIME_TAGS is absent or empty — exactly the intended precedence. Adversarial tests confirmed the alias works when canonical is truly unset, AutomaticEnv doesn't interfere, and invalid JSON in the alias is passed through without crashing Init.

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[anmarchenko]

E2E Test Report: SUCCESS

Tested by: Shepherd Agent (autonomous QA for Datadog Test Optimization)

Test Environment

• Method: Local testing with Shepherd rubocop playground and mockdog
• PR: [SDTEST-3871] Add runtime tags env alias #101
• Branch tested: anmarchenko/runtime-tags-env-alias
• Revision tested: 85c371f4629d15bac64c5d308eccf922a924bbb1

Results

Check	Status	Evidence
PR branch built and injected as ddtest	Passed	crook run rubocop -c ddtest-plan --dep ddtest=anmarchenko/runtime-tags-env-alias --debug completed successfully
DD_TEST_OPTIMIZATION_RUNTIME_TAGS alias was consumed by planner settings	Passed	Plan report showed Runtime tags: {"os.platform":"linux","runtime.version":"3.2.0"}
Runtime tag override reached skippable-tests request payload	Passed	TIA-enabled mockdog run captured /api/v2/ci/tests/skippable with configurations.os.platform=linux and configurations.runtime.version=3.2.0
Plan output remained valid	Passed	Focused plan produced 1 runner for spec/rubocop/cop/lint/unused_method_argument_spec.rb, skippable percentage 0.00

Issues Found

None.

Note: the first default mockdog run proved the alias was consumed by settings, but default mockdog settings have TIA disabled, so it did not call the skippable endpoint. I ran a second focused planner pass with the itr-discovery-only scenario to force the TIA/skippable path and verify the raw request body.

Verification

Datadog UI verification was not applicable for this change because the requested validation was ddtest plan and the run targeted local mockdog, not a real Datadog backend. The relevant backend-facing behavior was verified directly from mockdog's captured skippable request payload.

Test Methodology

1. Fetched PR details and inspected the diff.
2. Used the rubocop RSpec playground with ddtest-plan, matching this planner/settings-only change.
3. Ran with DD_TEST_OPTIMIZATION_RUNTIME_TAGS='{"os.platform":"linux","runtime.version":"3.2.0"}'.
4. Verified planner logs and report output showed the runtime tag override.
5. Re-ran with mockdog itr-discovery-only and a single spec file to exercise /api/v2/ci/tests/skippable.
6. Verified mockdog captured the expected runtime tag values in the request payload.

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This E2E test was performed by Shepherd - autonomous QA agent for Datadog Test Optimization.