test(transport): row 74 — gauge asserts become delta-over-scoped-action, not absolute
BundleSessionObservabilityTests' two gauge facts asserted absolute values (Assert.Equal(0, baseline), Assert.Equal(2, ReadGauge())) against what is a single process-global provider slot — the same latent shape as the row-32 QueueDepthGaugeTests flake, correct only while this file is the slot's sole registrant. Converted to the delta-over-scoped-action pattern the row-66 rejection-counter facts in the same file already use: a new ReadGaugeDelta helper measures how far the instrument MOVED across an action driven by this test's own store, so an inherited non-zero baseline cancels out. Two assertions got stronger in the process. The post-clear check was Assert.Equal(0, ReadGauge()) — "the instrument reports zero", which any unregistered slot satisfies; it is now "opening more sessions on the detached store moves the gauge by nothing", which is the actual claim. And the compare-and-clear fact gained a negative control: the superseded store's opens must NOT reach the instrument, so a slot still pointing at oldStore can no longer satisfy the assertion by coincidence when both stores hold equal counts. Fail-before (temporary probe, not committed): with a foreign provider returning 7 registered before the service starts, the OLD body fails `Assert.Equal(0, baseline)` with `Expected: 0 / Actual: 7`; the NEW delta body passes the identical scenario. Honest residual documented on the helper: a gauge has one slot and last-writer-wins, so a registrant that clobbers it BETWEEN the two reads is unrecoverable read-side — that needs row-32's mutual exclusion. It cannot arise today (this is the only file in the assembly constructing a BundleSessionEvictionService, and test assemblies are separate processes); a second such file should bring the collection treatment with it. Transport.Tests: 180/180 green.
This commit is contained in:
Joseph Doherty
+77
-16
@@ -215,30 +215,39 @@ public sealed class BundleSessionObservabilityTests
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public async Task EvictionService_RegistersTheGaugeProvider_AndClearsItOnStop()
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{
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// The eviction service is Transport's only lifecycle seam, so it owns the
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// process-global gauge slot. The gauge is read as a delta against a baseline
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// because the instrument is a process-wide static.
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// process-global gauge slot. Every assertion here is a DELTA over a scoped action
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// against this test's own store (register row 74) — see ReadGaugeDelta.
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var clock = new TestClock(DateTimeOffset.UtcNow);
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var store = new BundleSessionStore(Options.Create(new TransportOptions()), clock, NullLogger<BundleSessionStore>.Instance);
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var service = new BundleSessionEvictionService(store, NullLogger<BundleSessionEvictionService>.Instance);
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var baseline = ReadGauge();
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await service.StartAsync(CancellationToken.None);
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try
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{
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store.Open(SessionExpiringAt(clock.GetUtcNow().AddMinutes(30)));
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store.Open(SessionExpiringAt(clock.GetUtcNow().AddMinutes(30)));
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// While registered, this store's opens are what the gauge reports.
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var whileRegistered = ReadGaugeDelta(() =>
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{
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store.Open(SessionExpiringAt(clock.GetUtcNow().AddMinutes(30)));
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store.Open(SessionExpiringAt(clock.GetUtcNow().AddMinutes(30)));
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});
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Assert.Equal(2, ReadGauge());
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Assert.Equal(2, whileRegistered);
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}
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finally
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{
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await service.StopAsync(CancellationToken.None);
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}
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// After the clear the gauge falls back to reporting 0, not through a dead store.
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Assert.Equal(0, ReadGauge());
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Assert.Equal(0, baseline);
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// After the clear the gauge no longer reads through this store: opening more
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// sessions on it moves the instrument by nothing. Stated as a delta this is a
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// STRONGER claim than the old `Assert.Equal(0, ReadGauge())` — that one merely
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// said "the instrument reports zero", which any unregistered slot satisfies,
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// and which a foreign registrant would have failed for reasons unrelated to
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// the clear.
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var afterClear = ReadGaugeDelta(() =>
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store.Open(SessionExpiringAt(clock.GetUtcNow().AddMinutes(30))));
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Assert.Equal(0, afterClear);
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}
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[Fact]
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@@ -257,29 +266,81 @@ public sealed class BundleSessionObservabilityTests
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await newService.StartAsync(CancellationToken.None);
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try
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{
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newStore.Open(SessionExpiringAt(clock.GetUtcNow().AddMinutes(30)));
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// Late stop of the superseded instance.
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// Late stop of the superseded instance, then prove the NEWER store is still
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// the one driving the gauge — by moving it and measuring the movement.
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await oldService.StopAsync(CancellationToken.None);
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Assert.Equal(1, ReadGauge());
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var newStoreStillDrivesIt = ReadGaugeDelta(() =>
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newStore.Open(SessionExpiringAt(clock.GetUtcNow().AddMinutes(30))));
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Assert.Equal(1, newStoreStillDrivesIt);
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// Negative control on the same window: the superseded store is detached, so
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// its opens must not reach the instrument. Without this, a provider slot left
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// pointing at oldStore would still satisfy the assertion above by coincidence
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// whenever both stores happened to hold equal counts.
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var oldStoreIsDetached = ReadGaugeDelta(() =>
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oldStore.Open(SessionExpiringAt(clock.GetUtcNow().AddMinutes(30))));
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Assert.Equal(0, oldStoreIsDetached);
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}
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finally
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{
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await newService.StopAsync(CancellationToken.None);
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}
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Assert.Equal(0, ReadGauge());
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var afterClear = ReadGaugeDelta(() =>
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newStore.Open(SessionExpiringAt(clock.GetUtcNow().AddMinutes(30))));
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Assert.Equal(0, afterClear);
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}
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// ------------------------------------------------------------------
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// Helpers
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// ------------------------------------------------------------------
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/// <summary>
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/// Runs <paramref name="act"/> between two observations of the open-import-sessions
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/// gauge and returns how far the instrument MOVED across it.
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/// </summary>
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/// <remarks>
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/// <para>
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/// Register row 74. These tests used to assert absolute gauge values —
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/// <c>Assert.Equal(0, baseline)</c>, <c>Assert.Equal(2, ReadGauge())</c> — against
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/// what is a single process-global provider slot
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/// (<c>SetImportSessionCountProvider</c> / <c>ClearImportSessionCountProvider</c>).
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/// That is the same shape as the register row 32 flake in
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/// <c>QueueDepthGaugeTests</c>: correct only for as long as this file is the slot's
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/// sole registrant, and silently wrong the day a sibling suite writes it. A delta
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/// carries no assumption about what the slot held on entry, so a non-zero inherited
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/// baseline cancels out.
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/// </para>
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/// <para>
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/// Honest residual, and the reason this is a delta rather than a full fix: unlike
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/// <see cref="ReadRejectionCounter"/> — where every measurement in the window is
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/// driven synchronously by this test's own <c>Open</c> call, making it genuinely
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/// immune — a gauge has ONE slot and last-writer-wins. If a concurrent registrant
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/// overwrote the slot BETWEEN the two reads, no read-side technique could recover;
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/// that case needs mutual exclusion on the slot (row 32's serialized collection).
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/// It cannot arise today: this is the only file in the assembly that constructs a
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/// <c>BundleSessionEvictionService</c>, and test assemblies run in separate
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/// processes. A second such file should bring the collection treatment with it.
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/// </para>
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/// </remarks>
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/// <param name="act">The action to measure across.</param>
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/// <returns>The gauge's movement while <paramref name="act"/> ran.</returns>
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private static long ReadGaugeDelta(Action act)
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{
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var before = ReadGauge();
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act();
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return ReadGauge() - before;
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}
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/// <summary>
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/// Forces one synchronous observation of the open-import-sessions gauge and returns
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/// the measured value. Mirrors the MeterListener helper used by the Communication
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/// and StoreAndForward telemetry suites.
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/// and StoreAndForward telemetry suites. Private to <see cref="ReadGaugeDelta"/> by
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/// convention — see its remarks for why no test reads this absolutely.
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/// </summary>
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/// <returns>The gauge's current value, or 0 if it never reported.</returns>
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private static long ReadGauge()
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