test(metrics): initialize dirtyPods in TestModule_Reconcile modules

[Quang Nguyen (nddq)]

Description

TestModule_Reconcile builds four Module literals without dirtyPods — only InitModule initializes that field — and calls Reconcile on them. Reconcile calls run, which starts a ticker on the package constant interval (1 second, metrics_module.go:38) with a context that no test cancels. Each tick calls applyDirtyPods, and the first tick dereferences the nil *DirtyCache:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x21d3fe9]
github.com/microsoft/retina/pkg/common.(*DirtyCache).GetAddList(0x0)
        pkg/common/dirtycache.go:39
github.com/microsoft/retina/pkg/module/metrics.(*Module).applyDirtyPodsAdd(...)
        pkg/module/metrics/metrics_module.go:574

The SIGSEGV kills the whole test binary. Whether it fires is a race between the first tick and process exit: on a machine where the package takes longer than ~2 seconds, go test -tags=unit ./pkg/module/metrics/ fails every run.

This PR sets dirtyPods: common.NewDirtyCache() in the four literals, matching the neighboring TestPodCallBack and TestModule_NamespaceAndPodUpdates. Ticks on an empty cache are no-ops (no filtermanager calls), so the leaked run goroutines stay harmless for the remainder of the process.

Related Issue

N/A — found while validating #2628 locally.

Checklist

• I have read the contributing documentation.
• I signed and signed-off the commits (git commit -S -s ...). See this documentation on signing commits.
• I have correctly attributed the author(s) of the code.
• I have tested the changes locally.
• I have followed the project's style guidelines.
• I have updated the documentation, if necessary.
• I have added tests, if applicable. (N/A — fixes existing tests)

Screenshots (if applicable) or Testing Completed

At origin/main (792c9324) the panic reproduces on every run of the package on a VM where the suite takes ~2.5 seconds. With this fix, go test -tags=unit -count=10 ./pkg/module/metrics/ passes cleanly.

Additional Notes

go test -race on this package still fails for an unrelated pre-existing reason: TestBaseMetricObject's expire callback writes a test-local variable (basemetricsobject_test.go:54) that the test reads without synchronization (:77). It reproduces at origin/main with -run TestBaseMetricObject alone. CI does not run unit tests with -race, and that fix belongs in its own PR.

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Retina Code Coverage Report

Total coverage no change