Added a way to read what the AI received from your sources (#1100)

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

app/Tests/Chat/AttachingAFileAgainTests.cs

@@ -0,0 +1,64 @@
+using AIStudio.Chat;
+
+namespace AIStudio.Tests.Chat;
+
+/// <summary>
+/// Checks that a file attached again goes with its text as it is now, and only once.
+/// </summary>
+/// <remarks>
+/// A message being edited brings its attachments along, each with the text it was sent with. When
+/// the user changes the file and attaches it again, the message must not go with both texts.
+/// </remarks>
+[TestFixture]
+public sealed class AttachingAFileAgainTests
+{
+    private string testDirectory = string.Empty;
+
+    [SetUp]
+    public void CreateDirectory()
+    {
+        this.testDirectory = Path.Combine(Path.GetTempPath(), $"ai-studio-attach-again-{Guid.NewGuid():N}");
+        Directory.CreateDirectory(this.testDirectory);
+    }
+
+    [TearDown]
+    public void RemoveDirectory() => Directory.Delete(this.testDirectory, true);
+
+    [Test]
+    public void AFileAttachedAgainTakesThePlaceOfItsEarlierAttachment()
+    {
+        var path = Path.Combine(this.testDirectory, "minutes.txt");
+        File.WriteAllText(path, "The board met on Monday.");
+        var sentBefore = FileAttachment.FromPath(path) with { ProvenanceId = Guid.NewGuid() };
+        var otherFile = FileAttachment.FromPath(Path.Combine(this.testDirectory, "agenda.txt"));
+        var attachments = new HashSet<FileAttachment> { sentBefore, otherFile };
+
+        File.WriteAllText(path, "The board met on Monday and on Tuesday.");
+        attachments.AttachInPlaceOfSameFile(FileAttachment.FromPath(path));
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(attachments.Count(attachment => attachment.FilePath == path), Is.EqualTo(1), "The message would go with the old and the new text of the file.");
+            Assert.That(attachments.Single(attachment => attachment.FilePath == path).ProvenanceId, Is.Null, "Attaching a file again means the file as it is now.");
+            Assert.That(attachments, Does.Contain(otherFile));
+        });
+    }
+
+    [Test]
+    public void AFileOfTheSameTimeButAnotherSizeChanged()
+    {
+        var path = Path.Combine(this.testDirectory, "minutes.txt");
+        File.WriteAllText(path, "The board met on Monday.");
+        var writtenAt = File.GetLastWriteTimeUtc(path);
+        var before = FileVersion.Of(path);
+
+        // A file system which keeps the time coarsely, e.g., FAT, reports the same time after a quick change:
+        File.WriteAllText(path, "The board met on Monday and on Tuesday.");
+        File.SetLastWriteTimeUtc(path, writtenAt);
+
+        Assert.That(FileVersion.Of(path), Is.Not.EqualTo(before));
+    }
+
+    [Test]
+    public void AFileWhichIsGoneHasNoVersion() => Assert.That(FileVersion.Of(Path.Combine(this.testDirectory, "gone.txt")), Is.Null);
+}