https://spruce.corp.mongodb.com/task/mongo_node_driver_next_rhel80_large_Node22_test_9.0_replica_set_83668e620841398713a0fa64b2ed3205fb965152_26_09_07_10_41_28/logs?execution=0&sorts=STATUS%3AASC

[2026/09/07 13:03:25.392]   1 failing
[2026/09/07 13:03:25.392]   1) Client Backpressure (Prose)
[2026/09/07 13:03:25.392]        Test 5: Overload Errors with baseBackoffMS override base backoff:
[2026/09/07 13:03:25.392]       AssertionError: expected 299 to be at least 300
[2026/09/07 13:03:25.392]       + expected - actual
[2026/09/07 13:03:25.392]       -299
[2026/09/07 13:03:25.392]       +300
[2026/09/07 13:03:25.392]
[2026/09/07 13:03:25.392]       at Context.<anonymous> (test/integration/client-backpressure/client-backpressure.prose.test.ts:220:46)
[2026/09/07 13:03:25.392]       at processTicksAndRejections (node:internal/process/task_queues:103:5)

The assertion is an exact lower bound with no tolerance: with jitter pinned to 1 and baseBackoffMS=50, the two backoff sleeps are 100ms and 200ms, and the test requires the measured duration to be at least 300ms. The run came in 1ms short. measureDuration floors performance.now() on both ends, and Node timers run on a millisecond-granularity clock, so two chained setTimeout sleeps can complete marginally under the requested total as measured by performance.now(). The 600ms bound on the previous line (test/integration/client-backpressure/client-backpressure.prose.test.ts:219) can fail the same way. The bound comes from the spec pseudocode (assertGreaterEqual(with_base_backoff_ms_time, 0.3)), so a tolerance fix may belong in the specifications repo as well.

Summary of necessary driver changes

• Update backpressure prose test 5 to subtract a small tolerance (5ms) from the two lower duration bounds in step 10, per the commit below. Drivers MAY adjust the tolerance to fit the timing behavior of their platform. No functional driver changes - test-only.

Commits for syncing spec/prose tests
(and/or refer to an existing language POC if needed)

• https://github.com/mongodb/specifications/commit/9ecb35b1944ade6f7e711316f83c360bf045edfb

Context for other referenced/linked tickets

•  The flaky Node.js CI failure motivated this change.

AC

• Pull in prose test change (and text in comments), make sure it still runs and passes