Fix flaky ut TPDiskTest.ChunkWriteDifferentOffsetAndSize

[rosik]

Changelog category

• Not for changelog (changelog entry is not required)

Description for reviewers

• Close Mute ydb/core/blobstorage/pdisk/ut/TPDiskTest.ChunkWriteDifferentOffsetAndSize in main #34400

Flaky test:

VERIFY failed (2026-02-16T03:23:04.874435Z): Invalid random number range [0, 0)
  util/random/common_ops.h:50
  GenUniform(): requirement max > 0 failed
NPrivate::InternalPanicImpl(int, char const*, char const*, int, int, int, TBasicStringBuf<char, std::__y1::char_traits<char>>, char const*, unsigned long)+438 (0x24556C6)
NPrivate::Panic(NPrivate::TStaticBuf const&, int, char const*, char const*, char const*, ...)+263 (0x244C257)
NKikimr::GenParts(TReallyFastRng32&, unsigned long)+2428 (0x20AAE5C)
NKikimr::NTestSuiteTPDiskTest::ChunkWriteDifferentOffsetAndSizeImpl(bool, bool)+1843 (0x20F9523)
NKikimr::NTestSuiteTPDiskTest::TTestCaseChunkWriteDifferentOffsetAndSize::Execute_(NUnitTest::TTestContext&)+13 (0x20FA45D)
NKikimr::NTestSuiteTPDiskTest::TCurrentTest::Execute()::'lambda'()::operator()() const+71 (0x2124177)
NUnitTest::TTestBase::Run(std::__y1::function<void ()>, TBasicString<char, std::__y1::char_traits<char>> const&, char const*, bool)+120 (0x24E9ED8)
NKikimr::NTestSuiteTPDiskTest::TCurrentTest::Execute()+435 (0x2123B23)
NUnitTest::TTestFactory::Execute()+817 (0x24EA621)
NUnitTest::RunMain(int, char**)+3229 (0x24FCE4D)
??+0 (0x7F0754CCBD90)
__libc_start_main+128 (0x7F0754CCBE40)
_start+41 (0x2042029)

[ydbot]

Run Extra Tests

Run additional tests for this PR. You can customize:

• Test Size: small, medium, large (default: all)
• Test Targets: any directory path (default: ydb/)
• Sanitizers: ASAN, MSAN, TSAN
• Coredumps: enable for debugging (default: off)
• Additional args: custom ya make arguments

[Copilot]

Pull request overview

This PR fixes a flaky unit test TPDiskTest.ChunkWriteDifferentOffsetAndSize that had an 85.7% success rate due to a bug in random data generation. The issue was in the GenParts function which could cause an abort when calling rng.Uniform(0) in certain edge cases.

Changes:

• Fixed random part size generation to avoid calling Uniform with an empty range that would trigger an abort

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[github-actions]

⚪ 2026-02-18 18:56:21 UTC Pre-commit check linux-x86_64-relwithdebinfo for 7c50db8 has started.
⚪ 2026-02-18 18:56:38 UTC Artifacts will be uploaded here
⚪ 2026-02-18 18:58:55 UTC ya make is running...
🟢 2026-02-18 19:05:04 UTC Tests successful.

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
255	255	0	0	0	0

🟢 2026-02-18 19:05:12 UTC Build successful.

[github-actions]

⚪ 2026-02-18 18:56:52 UTC Pre-commit check linux-x86_64-release-asan for 7c50db8 has started.
⚪ 2026-02-18 18:57:10 UTC Artifacts will be uploaded here
⚪ 2026-02-18 18:59:23 UTC ya make is running...
🟢 2026-02-18 19:00:22 UTC Tests successful.

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
0	0	0	0	0	0

🟢 2026-02-18 19:00:28 UTC Build successful.

[github-actions]

🟢 2026-02-19 10:25:00 UTC The validation of the Pull Request description is successful.

[ydbot]

Backport

To backport this PR, click the button next to the target branch and then click "Run workflow" in the Run Actions UI.

Branch	Run
stable-25-3, stable-25-3-1, stable-25-4, stable-25-4-1
stable-25-4, stable-25-4-1
stable-25-4