[SDTEST-2713] Fix monorepo subdirectory path handling when ITR is enabled

[anmarchenko]

Summary

Fixes #33

• When running ddtest from a monorepo subdirectory (cd core && ddtest run), full test discovery (ITR enabled) returns repo-root-relative paths like core/spec/models/order_spec.rb. Workers run from the subdirectory CWD, so they resolve core/core/spec/... which does not exist.
• Added conservative path normalization in PrepareTestOptimization that detects the CWD's position relative to the git root and strips the matching prefix from repo-root-relative paths. Fail-safe: no-op if git root is unavailable, prefix doesn't match, or CWD is already repo root.
• Fast discovery path is unchanged (it already returns CWD-relative paths from glob).

E2E verification

• Run spree tests with ddtest both from repo root and from the core subfolder
• Make sure that backend skips at least one test suite completely
• Assert that tests are running successfully, that the test suite is skipped completely in both cases

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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 spree monorepo playground (core sub-project, ~5919 RSpec examples)
• Revision: 980cffe
• Backend: mockdog (local mock Datadog backend) with ITR skip scenarios
• ddtest branch: anmarchenko/fix_monorepo_subdirectory_tests

Results

Test	Command	Description	Status
From repo root	ddtest-core-root	Run ddtest from repo root with --tests-location "core/spec/**/*_spec.rb"	✅ PASSED
From subdirectory	ddtest-core	Run ddtest with cd core && ../bin/ddtest run	✅ PASSED

Details

Both runs used a mockdog scenario that marks 2 tests in role_spec.rb as skippable (ITR enabled). In both cases:

• ddtest correctly removed role_spec.rb from the worker split entirely — the file never appeared in any worker
• All 8 mockdog assertions passed: tests=5901, suites=421, sessions=4, modules=4, coverages=5865, telemetry valid
• Coverage collection was active and produced expected counts

Key difference between runs:

• From repo root, the skippable test suite name uses repo-root-relative path: Spree::Role at ./core/spec/models/spree/role_spec.rb
• From subdirectory, the skippable test suite name uses CWD-relative path: Spree::Role at ./spec/models/spree/role_spec.rb

The path normalization fix correctly handles both cases for test discovery and split distribution.

Test Methodology

1. Built ddtest from PR branch anmarchenko/fix_monorepo_subdirectory_tests
2. Used two mockdog scenarios with ITR enabled and role_spec.rb tests marked as skippable:
   • itr-spree-root-skip-role-spec — skippable test suite paths relative to repo root
   • itr-spree-core-skip-role-spec — skippable test suite paths relative to core/ subdirectory
3. Ran spree core tests with --debug flag in two configurations:
   • ddtest-core-root: from repo root with --tests-location "core/spec/**/*_spec.rb"
   • ddtest-core: with cd core && ../bin/ddtest run --framework rspec
4. Verified assertions against expected test/suite/coverage counts via mockdog report endpoint

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