Fix to ensure that at least one fc is active when total fcs < 3

[aks03dev]

Brief Description

Previously, for setups with fewer than 3 FCs, the existing shutdown formula could end up shutting down all FCs.

The number of FCs to shut down was calculated as:

n/2 + 1

For example, when n = 2:

2/2 + 1 = 2

This shuts down both FCs, which would not be a valid test scenario

Change Made

Updated the logic so that if the calculated shutdown count would bring down all FCs, the test shuts down n - 1 FCs instead.

[gemini-code-assist]

Summary of Changes

Hello, 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 refines the test for sampled backplane capacity counters by addressing an edge case where the test could inadvertently shut down all Fabric Cards (FCs) in systems with a small number of FCs. The changes ensure that the test always maintains at least one active FC, thereby preserving the validity of the test scenario and preventing unintended system states. Additionally, a check was added to ensure the test only runs when a sufficient number of FCs are available.

Highlights

• Test Logic Enhancement: Modified the test logic to prevent scenarios where all Fabric Cards (FCs) are shut down during testing, ensuring at least one FC remains active for valid test execution.
• Minimum FC Requirement: Introduced a new skip condition for the test, requiring a minimum of two removable Fabric Cards to proceed, preventing test execution in insufficient hardware configurations.

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[OpenConfigBot]

Pull Request Functional Test Report for #5259 / 349aa3b

Virtual Devices

Device	Test	Test Documentation	Job	Raw Log
Arista cEOS		gNMI-1.18: gNMI subscribe with sample mode for backplane capacity counters	99c273c6	Log
Cisco 8000E		gNMI-1.18: gNMI subscribe with sample mode for backplane capacity counters	873f1472	Log
Cisco XRd		gNMI-1.18: gNMI subscribe with sample mode for backplane capacity counters	bb156068	Log
Juniper ncPTX		gNMI-1.18: gNMI subscribe with sample mode for backplane capacity counters	3f182858	Log
Nokia SR Linux		gNMI-1.18: gNMI subscribe with sample mode for backplane capacity counters	043b9226	Log
Openconfig Lemming		gNMI-1.18: gNMI subscribe with sample mode for backplane capacity counters	3085b2d2	Log

Hardware Devices

Device	Test	Test Documentation	Raw Log
Arista 7808		gNMI-1.18: gNMI subscribe with sample mode for backplane capacity counters
Cisco 8808		gNMI-1.18: gNMI subscribe with sample mode for backplane capacity counters
Juniper PTX10008		gNMI-1.18: gNMI subscribe with sample mode for backplane capacity counters
Nokia 7250 IXR-10e		gNMI-1.18: gNMI subscribe with sample mode for backplane capacity counters

Help

[gemini-code-assist]

Code Review

This pull request enhances the TestOnChangeBackplaneCapacityCounters test by adding a pre-condition to skip the test if fewer than two fabric cards are available. It also introduces logic to ensure that at least one fabric card remains active during the test by capping the number of cards to be disabled. A review comment suggests improving the robustness of this capping logic by using a >= comparison instead of == for better future-proofing and clarity.

[gemini-code-assist]

For robustness and to better express the intent of never disabling all fabric cards, it's slightly better to use >= instead of == in your condition. While with the current logic fc cannot be greater than len(fabrics) for 2 or more fabrics, using >= makes the condition's purpose—to prevent shutting down all cards—more explicit and robust against potential future changes to the calculation of fc.

Suggested change

	if fc == len(fabrics) {
	fc = len(fabrics) - 1
	t.Logf("Capping fabric cards to disable at %d to keep at least 1 active", fc)
	}
	if fc >= len(fabrics) {
	fc = len(fabrics) - 1
	t.Logf("Capping fabric cards to disable at %d to keep at least 1 active", fc)
	}

[AmrNJ]

/fptest all