Fix: Mindwork Studio can miss the change from light to dark mode (#991)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/Tests/Tools/CircuitStateServiceTests.cs

@@ -0,0 +1,71 @@
+using AIStudio.Tools.Services;
+
+namespace AIStudio.Tests.Tools;
+
+/// <summary>
+/// Checks when the circuit state reports that the browser connection came back.
+/// </summary>
+/// <remarks>
+/// The report is there to fetch again what the browser sent while the connection was down, because Blazor
+/// drops it. The layout reads the color theme anew on it, for instance, since the machine may have switched
+/// its theme during sleep. So it has to come after every loss, and only then: missing one leaves the app
+/// with stale state, while a connection which was never lost has nothing to fetch again.
+/// </remarks>
+[TestFixture]
+public sealed class CircuitStateServiceTests
+{
+    [Test]
+    public void AConnectionWhichReturnsAfterALossIsReportedOnce()
+    {
+        var circuitState = new CircuitStateService();
+        var numReports = 0;
+        circuitState.ConnectionRestored += () => numReports++;
+
+        circuitState.MarkAsDisconnected();
+        circuitState.MarkAsConnected();
+
+        Assert.That(numReports, Is.EqualTo(1), "The connection was lost and came back, so whatever the browser sent in between is gone.");
+        Assert.That(circuitState.IsConnected, Is.True);
+    }
+
+    [Test]
+    public void TheFirstConnectionIsNotReported()
+    {
+        var circuitState = new CircuitStateService();
+        var numReports = 0;
+        circuitState.ConnectionRestored += () => numReports++;
+
+        circuitState.MarkAsConnected();
+
+        Assert.That(numReports, Is.Zero, "A circuit starts out connected, so its first connection has not lost anything.");
+    }
+
+    [Test]
+    public void AConnectionWhichWasNotLostIsNotReportedAgain()
+    {
+        var circuitState = new CircuitStateService();
+        var numReports = 0;
+        circuitState.ConnectionRestored += () => numReports++;
+
+        circuitState.MarkAsDisconnected();
+        circuitState.MarkAsConnected();
+        circuitState.MarkAsConnected();
+
+        Assert.That(numReports, Is.EqualTo(1), "The second call follows a connection which was up all along.");
+    }
+
+    [Test]
+    public void EveryLossIsReportedOnItsOwn()
+    {
+        var circuitState = new CircuitStateService();
+        var numReports = 0;
+        circuitState.ConnectionRestored += () => numReports++;
+
+        circuitState.MarkAsDisconnected();
+        circuitState.MarkAsConnected();
+        circuitState.MarkAsDisconnected();
+        circuitState.MarkAsConnected();
+
+        Assert.That(numReports, Is.EqualTo(2), "The machine went to sleep twice, and each time something may have been lost.");
+    }
+}