Tell whoever asked for a page what the search could not cover

app/Tests/Tools/RetrievalGapTests.cs

@@ -0,0 +1,38 @@
+using AIStudio.Tools.RAG;
+using AIStudio.Tools.Services;
+
+namespace AIStudio.Tests.Tools;
+
+/// <summary>
+/// Checks who hears about what kept a search from covering a local data source.
+/// </summary>
+/// <remarks>
+/// With Semantic Search, the model writes the query, not the user. A warning that the message was
+/// too long to search with would then blame the user for a query they never wrote, while the model,
+/// which could search with a shorter one, would learn nothing. Problems of the data source itself
+/// stay with the user either way, since nobody else can fix a missing embedding provider.
+/// </remarks>
+[TestFixture]
+public sealed class RetrievalGapTests
+{
+    [Test]
+    public void AQueryTheModelWroteIsNotTheUsersProblem()
+    {
+        Assert.That(DataSourceLocalRetrievalService.IsForTheUser(RetrievalGap.QUERY_NOT_SEARCHABLE, queryWrittenByUser: false), Is.False, "The model learns about it from the page and can search with a shorter query.");
+    }
+
+    [Test]
+    public void AMessageTheUserWroteIsTheirsToShorten()
+    {
+        Assert.That(DataSourceLocalRetrievalService.IsForTheUser(RetrievalGap.QUERY_NOT_SEARCHABLE, queryWrittenByUser: true), Is.True);
+    }
+
+    [TestCase(RetrievalGap.NOT_SEARCHED, false)]
+    [TestCase(RetrievalGap.NOT_SEARCHED, true)]
+    [TestCase(RetrievalGap.PARTLY_SEARCHED, false)]
+    [TestCase(RetrievalGap.PARTLY_SEARCHED, true)]
+    public void ProblemsOfTheDataSourceAreAlwaysForTheUser(RetrievalGap gap, bool queryWrittenByUser)
+    {
+        Assert.That(DataSourceLocalRetrievalService.IsForTheUser(gap, queryWrittenByUser), Is.True, "Only the user can fix an index or an embedding provider.");
+    }
+}