tests: fix nil panic in TestDisableSchedulingServiceFallback

[JmPotato]

What problem does this PR solve?

Issue Number: Close #8926

TestDisableSchedulingServiceFallback is flaky due to a nil pointer dereference inside an assert.Eventually callback. The test calls tc.GetPrimaryServer().GetCluster().IsBackgroundJobsRunning() without nil checks, causing a SIGSEGV panic when either GetPrimaryServer() or GetCluster() returns nil during the scheduling server's initialization window.

Additionally, the test used re.NotNil() (a require assertion) inside an Eventually callback. Since Eventually may run the callback in a goroutine context, calling FailNow() from a non-test goroutine can cause a panic.

What is changed and how does it work?

1. Replaced re.NotNil() require assertions inside the first Eventually callback with proper nil-check-and-return-false guards, preventing FailNow panics from non-test goroutines.
2. Added nil guards for GetPrimaryServer() and GetCluster() in the second Eventually callback before calling IsBackgroundJobsRunning(), matching the existing defensive pattern already used in the sibling test TestSchedulingServiceFallback.

Add nil guards in Eventually callbacks to prevent nil pointer dereference.
Replace re.NotNil() require assertions with nil-check-and-return-false
guards to avoid FailNow panics from non-test goroutines.

Check List

Tests

• Unit test

Release note

None.

[coderabbitai]

📝 Walkthrough

Walkthrough

Add defensive null checks in TestDisableSchedulingServiceFallback to prevent nil pointer dereferences when accessing server and cluster objects. Replace direct calls to GetServer() and GetRaftCluster() with guarded access patterns that safely return false if either is nil.

Changes

Cohort / File(s)	Summary
Flaky test stabilization tests/integrations/mcs/scheduling/server_test.go	Added defensive null checks in test callback to guard against nil dereferences on suite.pdLeader.GetServer() and GetRaftCluster(). Restructured call to IsSchedulingControllerRunning() with guarded sequential access pattern returning false if intermediate objects are nil.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• tikv/pd#10167 — Applies similar defensive nil-check refactoring patterns across test suites to eliminate flaky nil dereferences and timing issues

Suggested labels

size/S

Suggested reviewers

• bufferflies
• lhy1024
• rleungx

Poem

🐰 A nil that dared to rear its head,
Now guarded safe with checks instead,
No panic crashes in the night,
The flaky test shines stable and bright! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: fixing a nil panic in the TestDisableSchedulingServiceFallback test.
Linked Issues check	✅ Passed	The PR successfully addresses all coding requirements from issue #8926 by adding nil guards in Eventually callbacks and replacing require assertions with explicit nil-check guards to prevent panics.
Out of Scope Changes check	✅ Passed	All changes are scoped to fixing the test flakiness in TestDisableSchedulingServiceFallback; no unrelated modifications are present.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description check	✅ Passed	The PR description comprehensively addresses the problem, explains the root causes (nil pointer dereference and FailNow panics in goroutines), and details the exact changes made.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.80%. Comparing base (5885cec) to head (d29e625).
⚠️ Report is 16 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #10282    +/-   ##
========================================
  Coverage   78.80%   78.80%            
========================================
  Files         523      525     +2     
  Lines       70529    70824   +295     
========================================
+ Hits        55580    55815   +235     
- Misses      10955    10996    +41     
- Partials     3994     4013    +19     

Flag	Coverage Δ
unittests	78.80% <ø> (+<0.01%)	⬆️

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[JmPotato]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: okJiang

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Details

Needs approval from an approver in each of these files:

• OWNERS [okJiang]

Approvers can indicate their approval by writing /approve in a comment
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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-03-05 10:14:11.21012936 +0000 UTC m=+439495.788208544: ☑️ agreed by okJiang.

[okJiang]

/retest