ScadaBridge/tests/ZB.MOM.WW.ScadaBridge.Host.Tests/ScadaBridgeTelemetryTests.cs

using ZB.MOM.WW.ScadaBridge.Commons.Observability;

namespace ZB.MOM.WW.ScadaBridge.Host.Tests;

/// <summary>
/// Infrastructure-free guards for <see cref="ScadaBridgeTelemetry"/>: the meter name is the
/// stable value registered with OTel, and the emit helpers are safe to call (they are no-op
/// until follow-on tasks wire real emit points and a listener attaches).
/// </summary>
public class ScadaBridgeTelemetryTests
{
    [Fact]
    public void MeterName_IsStableValue()
    {
        Assert.Equal("ZB.MOM.WW.ScadaBridge", ScadaBridgeTelemetry.MeterName);
    }

    /// <summary>
    /// Register row 32 class: <c>SetQueueDepthProvider</c> writes the SAME process-global
    /// slot <c>QueueDepthGaugeCollection</c> (StoreAndForward.Tests) exists to serialize
    /// access to — this test was mutating it with no clear and no <c>[Collection]</c>,
    /// leaving a stray <c>() =&gt; 5</c> provider registered in the process for the rest of
    /// this assembly's run. Since the meter/instrument state is a single static field on
    /// <c>ScadaBridgeTelemetry</c> (Commons), the leak is scoped to whatever process this
    /// assembly's test host runs in — it cannot reach StoreAndForward.Tests (a separate
    /// assembly with its own test-host process), but it IS visible within Host.Tests, whose
    /// <c>MetricsEndpointTests</c> boots a real in-process host (<c>WebApplicationFactory</c>
    /// shares this AppDomain, not a child process) and scrapes <c>/metrics</c>, which
    /// enumerates every registered gauge including this one.
    ///
    /// Honesty note on what was and wasn't proven: a search of this assembly (and the whole
    /// test tree) found no test today that asserts on the VALUE of
    /// <c>scadabridge.store_and_forward.queue.depth</c> from Host.Tests or any other
    /// same-process reader — <c>MetricsEndpointTests</c> only asserts the endpoint returns
    /// Prometheus-shaped text, not this series' content, and the only test that DOES assert
    /// on the value (<c>QueueDepthGaugeTests</c>) lives in StoreAndForward.Tests, a distinct
    /// test-host process the leak cannot reach. So there is no currently-reproducible flake
    /// to demonstrate here (no fork of this test with the leak left in has an assertion to
    /// break) — the defect is a landmine for a FUTURE same-process reader, not a live one.
    /// The fix (compare-and-clear in <c>finally</c>) closes the landmine regardless; a
    /// <c>[Collection]</c> is intentionally not added since no second same-process reader of
    /// this slot exists to serialize against as of this writing — re-run this search before
    /// removing the guard below if that changes.
    /// </summary>
    [Fact]
    public void EmitHelpers_DoNotThrow()
    {
        Func<long> queueDepthProvider = () => 5;
        var ex = Record.Exception(() =>
        {
            ScadaBridgeTelemetry.RecordDeploymentApplied();
            ScadaBridgeTelemetry.RecordInboundApiRequest("X");
            ScadaBridgeTelemetry.SiteStreamSubscriberOpened();
            ScadaBridgeTelemetry.SiteStreamSubscriberClosed();
            ScadaBridgeTelemetry.LiveAlarmAggregatorStarted();
            ScadaBridgeTelemetry.LiveAlarmAggregatorStopped();
            ScadaBridgeTelemetry.RecordLiveAlarmStreamReconnect();
            ScadaBridgeTelemetry.SetQueueDepthProvider(queueDepthProvider);
        });

        try
        {
            Assert.Null(ex);
        }
        finally
        {
            // Compare-and-clear: only removes OUR delegate from the process-global slot, so
            // a legitimate concurrent registrant (a real StoreAndForwardService started
            // elsewhere in this process) is never stomped — mirrors
            // ScadaBridgeTelemetry.ClearQueueDepthProvider's own doc'd contract.
            ScadaBridgeTelemetry.ClearQueueDepthProvider(queueDepthProvider);
        }
    }
}