test(accordion): adding test coverage

[kdinev]

Description

Adding more test coverage.

Bug Fixes

• IgxAccordionComponent
  • When singleBranchExpand is set initially and the panels are rendered with @for, the panels collapsed on init no longer keep aria-expanded="true" and no ExpressionChangedAfterItHasBeenCheckedError is thrown in development mode.

Motivation / Context

The accordion had insufficient test coverage.

Type of Change (check all that apply):

• Bug fix
• New functionality
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactoring (no functional changes)
• Documentation
• Demos
• CI/CD
• Tests
• Changelog
• Skills/Agents

Component(s) / Area(s) Affected:

Accordion, Expansion Panel

How Has This Been Tested?

• Unit tests
• Manual testing
• Automated e2e tests

Test Configuration:

• Angular version:
• Browser(s):
• OS:

Screenshots / Recordings

Checklist:

• All relevant tags have been applied to this PR
• This PR includes unit tests covering all the new code (test guidelines)
• This PR includes API docs for newly added methods/properties (api docs guidelines)
• This PR includes feature/README.MD updates for the feature docs
• This PR includes general feature table updates in the root README.MD
• This PR includes CHANGELOG.MD updates for newly added functionality
• This PR contains breaking changes
• This PR includes ng update migrations for the breaking changes (migrations guidelines)
• This PR includes behavioral changes and the feature specification has been updated with them
• Accessibility (ARIA, keyboard navigation, focus management) has been verified

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused implementation is supported by coverage for the reported regression and related accordion behavior.

Review effort: Balanced
Findings: None

What changed in this PR

Fixes accordion initialization state synchronization and expands regression coverage.

Changes:

• Makes expansion-panel collapsed state signal-backed.
• Adds accordion lifecycle, navigation, cancellation, animation, and dynamic-panel tests.
• Documents the fix in the changelog.

File	Description
expansion-panel.component.ts	Reactively synchronizes collapsed state and ARIA bindings.
accordion.component.spec.ts	Adds comprehensive accordion regression coverage.
CHANGELOG.md	Records the initialization and ARIA fix.

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