AgentgatewayPolicy: Add frontend policy tests

[npolshakova]

The new frontend field on the AgentgatewayPolicy introduced in #12723 supports configuring:

• tcp
• tls
• http
• access logging
• tracing (todo, no translation logic)

Tasks:

• Add unit tests for missing subfields on the frontend policy under https://github.com/kgateway-dev/kgateway/tree/main/internal/kgateway/agentgatewaysyncer/testdata/inputs
• Add e2e tests for AgentgatewayPolicy frontend fields

For example, configuring access logs:

apiVersion: gateway.kgateway.dev/v1alpha1
kind: AgentgatewayPolicy
metadata:
  name: access-log-header
  namespace: default
spec:
  targetRefs:
    - group: gateway.networking.k8s.io
      kind: Gateway
      name: http-gw-for-test
  frontend:
    accessLog:
      attributes:
        add:
          - name: x-user-id
            expression: "request.headers['x-user-id']"

You should be able to send a request:

curl -i http://localhost:8080/get -H 'Host: www.example.com' H 'x-user-id: alice'

Then see the x-user-id: alice header logged in the agentgateway proxy logs.

[thc1006]

Working on this issue

Hi team,

I'm currently working on this issue and would like to share my implementation approach.

Implementation Plan

I'm planning to split this work into two focused pull requests to follow the Small CL principle and make reviews more manageable:

PR #1 (Ready for review): Unit Tests

• ✅ Add unit tests for all frontend policy subfields (TCP, TLS, HTTP, AccessLog)
• ✅ Test input YAML files in testdata/inputs/frontend/
• ✅ Golden output files for translation validation
• ✅ Test cases for combined configurations and edge cases
• Status: Ready to submit (~750 lines)

PR #2 (Planned): E2E Tests

• Create test/e2e/features/agentgateway_frontend/ test suite
• End-to-end validation following the backendconfigpolicy pattern
• Will be submitted after PR make individual known CRDs available #1 is reviewed

Rationale

This approach offers several benefits:

• Faster review cycles - Smaller, focused PRs are easier to review
• Early value delivery - Unit tests provide immediate validation
• Follows project patterns - Similar to how PR agentgateway: introduce new AgentgatewayPolicy CRD #12723 was followed by AgentgatewayPolicy: Add backend tests #12815, AgentgatewayPolicy: Add frontend policy tests #12816, AgentgatewayPolicy: Add Traffic policy tests #12817
• Maintains quality - All CI checks pass (verify, lint, tests)

Questions

Is this approach acceptable to the maintainers? I'm happy to combine them into a single PR if preferred, though it would be significantly larger (~1200+ lines).

Looking forward to your feedback!

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Related: Will open PR shortly with unit tests implementation