test(v2/driver): add test coverage for cache, validation, and helpers

[jsonmp-k8]

Summary

• Increase test coverage for the backend/src/v2/driver package from 29.8% to 36.7% by adding 58 new test cases targeting previously untested functions
• Add tests for cache subsystem (getFingerPrint, getFingerPrintsAndID, createCache) with a mock cacheutils.Client
• Add validation tests for validateContainer, validateDAG, validateRootDAG, validateNonRoot
• Add tests for helper functions (inputParamConstant, inputParamComponent, inputParamTaskOutput, getItems)
• Add tests for provisionOutputs and InferIndexedTaskName

Test plan

• All 58 new test cases pass with go test -v -cover ./backend/src/v2/driver/...
• No existing tests broken
• Coverage verified at 36.7% (up from 29.8%)

[google-oss-prow]

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[github-actions]

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[Copilot]

Pull request overview

Adds targeted unit tests to improve coverage in backend/src/v2/driver, focusing on previously untested helper, validation, caching, and resolution logic.

Changes:

• Added new unit tests for driver validation paths (validateContainer, validateDAG, validateRootDAG, validateNonRoot).
• Added new unit tests for caching helpers (getFingerPrint, getFingerPrintsAndID, createCache) using a mock cacheutils.Client.
• Added/extended unit tests for misc helpers (inputParam*, getItems, provisionOutputs, InferIndexedTaskName).

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
backend/src/v2/driver/util_test.go	Adds tests for input-param helper constructors and getItems.
backend/src/v2/driver/root_dag_test.go	New tests for validateRootDAG option validation.
backend/src/v2/driver/resolve_test.go	Adds tests for InferIndexedTaskName.
backend/src/v2/driver/driver_test.go	Adds tests for validateNonRoot and provisionOutputs.
backend/src/v2/driver/dag_test.go	New tests for validateDAG option validation.
backend/src/v2/driver/container_test.go	New tests for validateContainer option validation.
backend/src/v2/driver/cache_test.go	New tests for cache fingerprinting and cache entry creation with a mock client.

🤖 LGTM 🤖

[jsonmp-k8]

/ok-to-test