Auto: ablegacy-10 — diagnostic counters as tags

Closes #253

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/AbLegacyDiagnosticsIntegrationTests.cs

@@ -0,0 +1,56 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.PlcFamilies;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests;
+
+/// <summary>
+///     PR ablegacy-10 / #253 — wire-level smoke against ab_server PCCC: after N reads
+///     against the live runtime, the auto-emitted <c>_Diagnostics/&lt;host&gt;/RequestCount</c>
+///     short-circuit must round-trip the same N value through <c>ReadAsync</c>. Skipped
+///     when ab_server isn't reachable; otherwise builds the same way the existing read
+///     smoke tests do.
+/// </summary>
+[Collection(AbLegacyServerCollection.Name)]
+[Trait("Category", "Integration")]
+[Trait("Simulator", "ab_server-PCCC")]
+public sealed class AbLegacyDiagnosticsIntegrationTests(AbLegacyServerFixture sim)
+{
+    [AbLegacyFact]
+    public async Task RequestCount_diagnostic_matches_read_invocations()
+    {
+        if (sim.SkipReason is not null) Assert.Skip(sim.SkipReason);
+
+        var deviceUri = $"ab://{sim.Host}:{sim.Port}/{sim.CipPath}";
+        await using var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions(deviceUri, AbLegacyPlcFamily.Slc500)],
+            Tags =
+            [
+                new AbLegacyTagDefinition(
+                    Name: "IntCounter",
+                    DeviceHostAddress: deviceUri,
+                    Address: "N7:0",
+                    DataType: AbLegacyDataType.Int),
+            ],
+            Timeout = TimeSpan.FromSeconds(5),
+            Probe = new AbLegacyProbeOptions { Enabled = false },
+        }, driverInstanceId: "ablegacy-smoke-diagnostics");
+
+        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);
+
+        const int N = 5;
+        for (var i = 0; i < N; i++)
+            await drv.ReadAsync(["IntCounter"], TestContext.Current.CancellationToken);
+
+        // Diagnostic short-circuit returns the live counter through ReadAsync without a
+        // libplctag round-trip. Verifies both that the discovery path emitted the
+        // address + that the read path serves it locally with Good status.
+        var diagRef = $"{AbLegacyDiagnosticTags.DiagnosticsFolderPrefix}{deviceUri}/RequestCount";
+        var snapshots = await drv.ReadAsync([diagRef], TestContext.Current.CancellationToken);
+
+        snapshots.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.Good);
+        Convert.ToInt64(snapshots.Single().Value).ShouldBe(N);
+    }
+}