[Misc] Added unit test for APA post autoscaler

[nurali-techie]

Pull Request Description

There is a need to improve unit test coverage for pod autoscaler controller. With this PR, we are adding unit tests for APA algo.

Related Issues

Resolves: part of [#1649] (APA unit tests)

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[gemini-code-assist]

Summary of Changes

Hello @nurali-techie, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the robustness of the pod autoscaler by introducing a comprehensive suite of unit tests for the APA (Adaptive Pod Autoscaler) algorithm. It also improves the overall testability and code organization by refactoring the mock scaling context into a dedicated, reusable file and internalizing the base scaling context within its package. These changes collectively contribute to better maintainability and reliability of the autoscaling logic.

Highlights

• New Unit Tests for APA Algorithm: Comprehensive unit tests have been added for the APAAlgorithm.computeTargetReplicas function, covering various scaling scenarios including basic scale-up/down, rate limiting, and tolerance checks.
• Refactored Test Mocking: A dedicated mockScalingContext has been introduced in its own file (mock_context_test.go) to centralize and improve reusability of the ScalingContext mock across different autoscaler algorithm tests.
• Internalized Base Scaling Context: The BaseScalingContext struct in pkg/controller/podautoscaler/context/context.go has been renamed to baseScalingContext (unexported), making it an internal implementation detail of the package.
• Minor Type Correction in APA Algorithm: Type casting for maxScaleUp and maxScaleDown variables in apa.go was adjusted from float64 to int32 to ensure consistency in scaling calculations.

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[gemini-code-assist]

Code Review

This pull request is a valuable contribution, adding unit tests for the APA autoscaler algorithm and improving overall test coverage. The refactoring work is also well-executed: extracting the mock scaling context into a shared file is a great way to reduce code duplication, and making BaseScalingContext unexported improves encapsulation within the context package. The logic simplification in apa.go is also a welcome improvement.

I have one suggestion regarding context.go to further enhance encapsulation. Additionally, as a minor process note, the PR title prefix [Test] doesn't seem to be in the list of approved prefixes in your contribution guidelines. You may want to adjust it.

[gemini-code-assist]

To improve encapsulation and hide implementation details from consumers of this package, it's a best practice for exported factory functions to return an interface type. In this case, NewBaseScalingContext should return ScalingContext instead of the concrete (and now unexported) type *baseScalingContext.

Suggested change

	func NewBaseScalingContext() *baseScalingContext {
	func NewBaseScalingContext() ScalingContext {

[nurali-techie]

There are two method in baseScalingContext which is not defined for ScalingContext. These two methods are used in code so we can't incorporate this suggestion before adding thoese two method.

Two methods -- SetMinReplicas(), SetMaxReplicas()

For now, I think we can ignore this minor suggestion.

[googs1025]

we should all use ScalingContext interface instead of BaseScalingContext. so change BaseScalingContext -> baseScalingContext make sense to me

[nurali-techie]

@googs1025 this PR is ready for review. Below is the details on the change made commit by commit so it's easy to review.

commit1 -- refactor: move mock context to new file
I have moved mockScalingContext to new file as it is now getting used by multiple tests (KPA, APA). I have alos made baseScalingContext to private from public to make sure that we always use NewBaseScalingContext() to create new instance.

commit2 -- test: added test for APA scaling algo
This has the main unit tests changes.

commit3 -- refactor: remove unnecessary type cast for better code readability
I see that unnecessary type cast is done in APA computeTargetReplicas(). So removed them for better code readability.

[googs1025]

I want to make sure one thing: we convert from float -> int to ensure the stability of the unit test, right?

[nurali-techie]

I am not quite sure on what you are referring about stability of unit test. Unit tests will work without this change (commit_link).

This change is made for better code readability. If you see, math.Ceil() and math.Floor() always return int (check documentation) so it's safe to type cast to int.

Once we type cast both variable maxScaleUp and expectedPods to int; we can work with them without any further type cast which simplify the code and improve readability.

[Jeffwan]

technically, math,Ceil() math.Floor() still return float but it's integer. The refactoring is about earlier type conversion, not about the return types here. so this is still ok

[Jeffwan]

@googs1025 need your input here. If it looks good to you, feel free to merge it

[googs1025]

will final review today

[googs1025]

LGTM