Kept the unsent message with its chat (#1049)

app/Tests/Components/ChatComposerStateTests.cs

@@ -0,0 +1,64 @@
+using AIStudio.Chat;
+using AIStudio.Components;
+using AIStudio.Settings;
+
+namespace AIStudio.Tests.Components;
+
+/// <summary>
+/// Checks what the composer counts as a message the user started.
+/// </summary>
+/// <remarks>
+/// That decides whether a chat template may still fill the composer, and whether leaving the chat
+/// warns about unsaved changes. A draft brought back from a chat is always the user's own, while a
+/// chat template only suggests a message.
+/// </remarks>
+[TestFixture]
+public sealed class ChatComposerStateTests
+{
+    [Test]
+    public void ADraftBroughtBackIsTheMessageOfTheUser()
+    {
+        var draft = new ChatDraft();
+        draft.SetText("Summarize the meeting");
+        draft.AddAttachments([new FileAttachment(FileAttachmentType.DOCUMENT, "agenda.pdf", "/documents/agenda.pdf", 1024)]);
+        var composer = new ChatComposerState();
+
+        composer.RestoreFromDraft(draft);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(composer.UserInput, Is.EqualTo("Summarize the meeting"));
+            Assert.That(composer.FileAttachments.Select(attachment => attachment.FilePath), Is.EqualTo(new[] { "/documents/agenda.pdf" }));
+            Assert.That(composer.HasUserDraft, Is.True, "A chat template must not replace the message the user came back to.");
+        });
+    }
+
+    [Test]
+    public void AnEmptyDraftLeavesTheComposerFree()
+    {
+        var composer = new ChatComposerState();
+        composer.SetUserInput("A message of the chat before");
+
+        composer.RestoreFromDraft(new ChatDraft());
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(composer.UserInput, Is.Empty, "The message of the chat before belongs to that chat.");
+            Assert.That(composer.HasUserDraft, Is.False, "Nobody started a message in this chat, so a chat template may still fill the composer.");
+        });
+    }
+
+    [Test]
+    public void TheMessageOfAChatTemplateIsNoDraftOfTheUser()
+    {
+        var composer = new ChatComposerState();
+
+        composer.ApplyTemplate(new ChatTemplate { PredefinedUserPrompt = "Translate the following text:" });
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(composer.UserInput, Is.EqualTo("Translate the following text:"));
+            Assert.That(composer.HasUserDraft, Is.False, "Leaving the chat must not warn about a message the user never wrote.");
+        });
+    }
+}