Fixed Semantic Search with external data sources (ERI servers) (#1090)

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

app/Tests/Tools/ERIServerRulesTests.cs

@@ -0,0 +1,49 @@
+using AIStudio.Tools.ERIClient.DataModel;
+using AIStudio.Tools.Services;
+
+namespace AIStudio.Tests.Tools;
+
+/// <summary>
+/// Checks which providers the server of an ERI data source allows to see its data.
+/// </summary>
+/// <remarks>
+/// The operator of the server owns the data, so the rule of the server applies on top of the
+/// security policy configured in AI Studio, and to a trusted provider as well. Until now, a trusted
+/// provider skipped the rule of the server altogether, so a server which allows no provider at all
+/// stayed open to it.
+/// </remarks>
+[TestFixture]
+public sealed class ERIServerRulesTests
+{
+    [TestCase(true)]
+    [TestCase(false)]
+    public void AServerForAnyProviderAllowsEveryProvider(bool usingTrustedProvider)
+    {
+        Assert.That(DataSourceService.ServerAllows(new SecurityRequirements(ProviderType.ANY), usingTrustedProvider), Is.True);
+    }
+
+    [Test]
+    public void AServerForSelfHostedProvidersAllowsOnlyATrustedOne()
+    {
+        var requirements = new SecurityRequirements(ProviderType.SELF_HOSTED);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(DataSourceService.ServerAllows(requirements, usingTrustedProvider: true), Is.True);
+            Assert.That(DataSourceService.ServerAllows(requirements, usingTrustedProvider: false), Is.False);
+        });
+    }
+
+    [TestCase(true)]
+    [TestCase(false)]
+    public void AServerWithoutAllowedProvidersAllowsNone(bool usingTrustedProvider)
+    {
+        Assert.That(DataSourceService.ServerAllows(new SecurityRequirements(ProviderType.NONE), usingTrustedProvider), Is.False, "The operator closed the data source, and a trusted provider is no exception.");
+    }
+
+    [Test]
+    public void AnUnknownRuleAllowsNoProvider()
+    {
+        Assert.That(DataSourceService.ServerAllows(new SecurityRequirements((ProviderType)99), usingTrustedProvider: true), Is.False, "Better safe than sorry.");
+    }
+}