Highlighted code blocks inside the app (#1153)

app/Tests/Components/HighlightedMarkdownTests.cs

@@ -0,0 +1,23 @@
+using AIStudio.Components;
+using AIStudio.Tools;
+
+using Markdig.Syntax;
+
+namespace AIStudio.Tests.Components;
+
+/// <summary>
+/// Checks the text which a code block AI Studio highlights itself shows and copies.
+/// </summary>
+[TestFixture]
+public sealed class HighlightedMarkdownTests
+{
+    [TestCase("```python\nprint(1)\n\nx = 2\n```", "print(1)\n\nx = 2")]
+    [TestCase("```python\r\nprint(1)\r\n\r\nx = 2\r\n```", "print(1)\r\n\r\nx = 2", Description = "Every line keeps its line break, the empty ones, too.")]
+    [TestCase("```python\n    indented\n```", "    indented", Description = "The indentation is a part of the code.")]
+    [TestCase("```python\n```", "", Description = "An empty block has no text.")]
+    public void ACodeBlockShowsItsLines(string markdown, string expected)
+    {
+        var block = Markdig.Markdown.Parse(markdown, Markdown.CHAT_MARKDOWN_PIPELINE).Descendants<FencedCodeBlock>().Single();
+        Assert.That(HighlightedMarkdown.TextOf(block), Is.EqualTo(expected));
+    }
+}