tests: add unit tests for DAG builder

[skynetigor]

Summary

closes: #13412

• Introduce AtomicGraphNode
• Add unit-tests for converting If condition step into DAG
• Add unit-tests for converting Foreach step into DAG
• Tests for other steps have to be done in along with step implementation

Checklist

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• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• If a plugin configuration key changed, check if it needs to be allowlisted in the cloud and added to the docker list
• This was checked for breaking HTTP API changes, and any breaking changes have been approved by the breaking-change committee. The release_note:breaking label should be applied in these situations.
• Flaky Test Runner was used on any tests changed
• The PR description includes the appropriate Release Notes section, and the correct release_note:* label is applied per the guidelines
• Review the backport guidelines and apply applicable backport:* labels.

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Describe the risk, its severity, and mitigation for each identified risk. Invite stakeholders and evaluate how to proceed before merging.

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[Copilot]

Pull Request Overview

This PR adds comprehensive unit tests for the DAG builder component, which converts workflow steps into executable graphs. The changes primarily focus on testing the conversion logic for conditional (If) and loop (Foreach) steps, along with atomic steps.

• Add unit tests for converting atomic, If condition, and Foreach steps into DAG structures
• Refactor the DAG building logic to properly handle atomic steps with a new AtomicGraphNode type
• Update function signatures to accept WorkflowSchema instead of WorkflowExecutionEngineModel

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
build_execution_graph.test.ts	Comprehensive test suite covering atomic, if, foreach, and complex workflow scenarios
build_execution_graph.ts	Refactored to support atomic step nodes and improved step visiting logic
workflow_task_runner.ts	Updated to pass workflow.definition.workflow to graph converter
scheduler_service.ts	Updated to pass workflow.definition.workflow to graph converter
step_factory.ts	Added support for atomic step implementation and removed fallback to connector step
atomic_step_impl.ts	New implementation for atomic workflow steps
base.ts	Added AtomicGraphNode schema and type definitions
Various type files	Updated exports to include new AtomicGraphNode type

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 0259e95

Metrics [docs]

Public APIs missing comments

Total count of every public API that lacks a comment. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats comments for more detailed information.

id	before	after	diff
@kbn/workflows	154	156	+2

Unknown metric groups

API count

id	before	after	diff
@kbn/workflows	155	157	+2

History

• 💛 Build #326611 was flaky 4287609
• 💔 Build #326526 failed 6cdb5e0
• 💚 Build #326413 succeeded 5a29af0

[Kiryous]

LGTM