test/integration: introduce robust harness and migrate EPP suite

[LukeAVanDrie]

What type of PR is this?
/kind test
/kind cleanup

What this PR does / why we need it:

This PR completes the migration of the integration test suite to the new isolated harness architecture. Following the pattern established in the Body-Based Routing (BBR) migration (#1959), this PR overhauls the EPP hermetic test suite.

The EPP tests are significantly more complex than BBR as they involve the full Kubernetes Controller Runtime lifecycle (Manager, Informers, Caches) and the Scheduler logic. This refactor introduces strict namespace isolation to prevent resource pollution between test cases and promotes server lifecycle logic to shared utilities. This will also be useful for future Flow Control tests which must modify pod metrics to toggle between saturated and unsaturated pool states.

Key Improvements

1. Namespace-Scoped Controller Manager:

   • Introduces TestHarness, which generates a unique Namespace (via UUID) for every test case.
   • Configures the controller-runtime Manager with a namespace-scoped cache. This ensures that the EPP server under test only sees Pods and Pools relevant to the current test case, eliminating "ghost" resources from previous runs affecting scheduling decisions.
   • Note: EPP tests currently run serially (t.Parallel() is disabled) because they rely on the singleton global Prometheus registry.

2. Domain-Specific Language (DSL):

   • Introduces EPP-specific builders in epp/util_test.go (e.g., ReqSubset, P() for pod states) and assertions (e.g., ExpectRouteTo, ExpectBufferResp).
   • Reduces visual noise in table-driven tests, making the scheduling logic (Queue vs. KV Cache vs. LoRA Affinity) immediately obvious.

3. Deterministic Synchronization:

   • Adds WaitForReadyPodsMetric. This blocks test execution until the internal scheduler state (via Prometheus metrics) matches the Kubernetes API state, preventing race conditions where requests are sent before the scheduler has indexed the backend pods.

4. Shared Infrastructure:

   • Promotes server lifecycle logic (startup, strict 127.0.0.1 binding, TCP readiness checks) to the shared test/integration package.
   • Updates the existing BBR harness to use these shared utilities, reducing boilerplate.

Refactoring Note

test/integration/util.go still retains some logic specific to the EPP domain. While these belong conceptually in test/integration/epp/util_test.go, I opted to keep them in the shared util.go package for this PR to minimize the already large diff size.

Test Coverage Mapping

Old Test Case Name	New Test Case Name	Changes / Notes
Standard Routing Logic
select lower queue and kv cache, no active lora	select lower queue and kv cache	Direct mapping.
select active lora, low queue	select active lora, low queue	Direct mapping.
select lora despite higher kv cache usage	select lora despite higher kv cache (affinity)	Direct mapping.
don't shed requests by default	do not shed requests by default	Direct mapping.
Error Handling & Protocol
invalid json; return body	invalid json body	Direct mapping.
body sent over multiple requests...	split body across chunks	Renamed for clarity. Tests that EPP correctly reassembles fragmented JSON bodies.
no backend pods are available	no backend pods available	Direct mapping.
request don't contains invalid payload, model not exist	request missing model field	Renamed to fix grammar; asserts 400 when JSON is valid but missing mandatory fields.
simple GET Request	protocol: simple GET (header only)	Renamed to clarify intent.
Subsetting & Metadata
select active lora with subsetting tag, all pods available	subsetting: select best from subset	Renamed for clarity.
select active lora with subsetting tag, some pods match	subsetting: partial match	Renamed for clarity.
select active lora with subsetting tag, no pods available	subsetting: no pods match	Renamed for clarity.
Passthrough & Rewrites
inferenceobjective's modelName is not translated, passthrough	passthrough: model not in objectives	Renamed for clarity.
rewrite request model	rewrite request model	Direct mapping.
Response Processing
responsebody sent over multiple requests, content-type is json, buffer	response buffering: multi-chunk JSON	Renamed for clarity.
Response is invalid json; return body	response buffering: invalid JSON	Renamed for clarity.
responsebody sent over a single request... (JSON variant)	response buffering: empty EOS chunk (JSON)	Renamed. Old name was verbose; tests Envoy behavior of sending empty data frame to signal EOS.
responsebody sent over a single request... (SSE variant)	response streaming: SSE token counting	Renamed. Old name was a duplicate copy-paste error; tests token counting logic on SSE streams.

Which issue(s) this PR fixes:
Refactoring groundwork necessary to support complex state-mutation tests (e.g., Flow Control) which require a strictly isolated environment.

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

@LukeAVanDrie: The label(s) kind/test cannot be applied, because the repository doesn't have them.

Details

In response to this:

What type of PR is this?
/kind test
/kind cleanup

What this PR does / why we need it:

This PR completes the migration of the integration test suite to the new isolated harness architecture. Following the pattern established in the Body-Based Routing (BBR) migration, this PR overhauls the EPP hermetic test suite.

The EPP tests are significantly more complex than BBR as they involve the full Kubernetes Controller Runtime lifecycle (Manager, Informers, Caches) and the Scheduler logic. This refactor introduces strict namespace isolation to prevent resource pollution between test cases and promotes server lifecycle logic to shared utilities. This will also be useful for future Flow Control tests which must modify pod metrics to toggle between saturated and unsaturated pool states.

Key Improvements

1. Namespace-Scoped Controller Manager:

• Introduces TestHarness, which generates a unique Namespace (via UUID) for every test case.
• Configures the controller-runtime Manager with a namespace-scoped cache. This ensures that the EPP server under test only sees Pods and Pools relevant to the current test case, eliminating "ghost" resources from previous runs affecting scheduling decisions.
• Note: EPP tests currently run serially (t.Parallel() is disabled) because they rely on the singleton global Prometheus registry.

2. Domain-Specific Language (DSL):

• Introduces EPP-specific builders in epp/util_test.go (e.g., ReqSubset, P() for pod states) and assertions (e.g., ExpectRouteTo, ExpectBufferResp).
• Reduces visual noise in table-driven tests, making the scheduling logic (Queue vs. KV Cache vs. LoRA Affinity) immediately obvious.

3. Deterministic Synchronization:

• Adds WaitForReadyPodsMetric. This blocks test execution until the internal scheduler state (via Prometheus metrics) matches the Kubernetes API state, preventing race conditions where requests are sent before the scheduler has indexed the backend pods.

4. Shared Infrastructure:

• Promotes server lifecycle logic (startup, strict 127.0.0.1 binding, TCP readiness checks) to the shared test/integration package.
• Updates the existing BBR harness to use these shared utilities, reducing boilerplate.

Refactoring Note

test/integration/util.go still retains some logic specific to the EPP domain. While these belong conceptually in test/integration/epp/util_test.go, I opted to keep them in the shared util.go package for this PR to minimize the already large diff size.

Test Coverage Mapping

Old Test Case Name	New Test Case Name	Changes / Notes
Standard Routing Logic
select lower queue and kv cache, no active lora	select lower queue and kv cache	Direct mapping.
select active lora, low queue	select active lora, low queue	Direct mapping.
select lora despite higher kv cache usage	select lora despite higher kv cache (affinity)	Direct mapping.
don't shed requests by default	do not shed requests by default	Direct mapping.
Error Handling & Protocol
invalid json; return body	invalid json body	Direct mapping.
body sent over multiple requests...	split body across chunks	Renamed for clarity. Tests that EPP correctly reassembles fragmented JSON bodies.
no backend pods are available	no backend pods available	Direct mapping.
request don't contains invalid payload, model not exist	request missing model field	Renamed to fix grammar; asserts 400 when JSON is valid but missing mandatory fields.
simple GET Request	protocol: simple GET (header only)	Renamed to clarify intent.
Subsetting & Metadata
select active lora with subsetting tag, all pods available	subsetting: select best from subset	Renamed for clarity.
select active lora with subsetting tag, some pods match	subsetting: partial match	Renamed for clarity.
select active lora with subsetting tag, no pods available	subsetting: no pods match	Renamed for clarity.
Passthrough & Rewrites
inferenceobjective's modelName is not translated, passthrough	passthrough: model not in objectives	Renamed for clarity.
rewrite request model	rewrite request model	Direct mapping.
Response Processing
responsebody sent over multiple requests, content-type is json, buffer	response buffering: multi-chunk JSON	Renamed for clarity.
Response is invalid json; return body	response buffering: invalid JSON	Renamed for clarity.
responsebody sent over a single request... (JSON variant)	response buffering: empty EOS chunk (JSON)	Renamed. Old name was verbose; tests Envoy behavior of sending empty data frame to signal EOS.
responsebody sent over a single request... (SSE variant)	response streaming: SSE token counting	Renamed. Old name was a duplicate copy-paste error; tests token counting logic on SSE streams.

Which issue(s) this PR fixes:
Refactoring groundwork necessary to support complex state-mutation tests (e.g., Flow Control) which require a strictly isolated environment.

Does this PR introduce a user-facing change?:

NONE

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[k8s-ci-robot]

Hi @LukeAVanDrie. Thanks for your PR.

I'm waiting for a github.com member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[LukeAVanDrie]

/assign @ahg-g

I included a test mapping in the PR description which should hopefully make reviewing hermetic_test.go a bit easier. It's probably best to review as a full rewrite. I have ensured existing test cases and assertions strictly match.

[ahg-g]

/ok-to-test

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: LukeAVanDrie
Once this PR has been reviewed and has the lgtm label, please ask for approval from ahg-g. For more information see the Code Review Process.

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[LukeAVanDrie]

Fixed the boilerplate issue on last push.

[LukeAVanDrie]

resolved merge conflict after rebasing