Fix ShouldContainHtml comparing actual HTML to itself (#3346)

* Fix ShouldContainHtml comparing actual HTML to itself

expectedCompare was built from `actual` instead of `expected`, causing
the assertion to always pass regardless of whether the expected fragment
was present in the actual output.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

* Fix inline image renderer emitting alt text as title unconditionally

The renderer was always writing title="<alt>" for every image, ignoring
the actual title parsed from the markdown title syntax. This caused all
images to get a spurious title attribute, and made it impossible for
explicit titles from "My Title =50%" syntax to appear correctly.

Use link.Title (already correctly set by ParseStylingInstructions) and
only emit the title attribute when it is non-empty.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

* Align C# inline image tests with authoring test ground truth

The F# authoring tests (the ground truth) document that inline images
always use alt text as the title attribute — even when an explicit title
is supplied in the markdown title syntax. The renderer behaviour was
correct; the C# xUnit expectations were wrong (missing title, or using
the parsed title instead of alt text) and had been silently passing
because of the ShouldContainHtml bug fixed in the previous commit.

Restore the renderer to always write title from alt text and update the
C# tests to match.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: Mpdreamz

src/Elastic.Markdown/Myst/Renderers/HtmxLinkInlineRenderer.cs

@@ -94,7 +94,7 @@ private static void WriteImage(HtmlRenderer renderer, LinkInline link)
 		// Write any additional attributes (like width/height from styling instructions)
 		_ = renderer.WriteAttributes(link);
 
-		// Set title to alt text for inline images (after any substitutions are processed)
+		// Always use alt text as title for accessibility consistency
 		if (link.FirstChild != null)
 		{
 			_ = renderer.Write(" title=\"");

tests/Elastic.Markdown.Tests/Inline/InlineImageTest.cs

@@ -19,7 +19,7 @@ public class InlineImageTest(ITestOutputHelper output) : InlineTest<LinkInline>(
 	public void GeneratesAttributesInHtml() =>
 		// language=html
 		Html.ShouldContainHtml(
-			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" /></p>"""
+			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" title="Elasticsearch" /></p>"""
 		);
 }
 
@@ -36,7 +36,7 @@ public class RelativeInlineImageTest(ITestOutputHelper output) : InlineTest<Link
 	public void GeneratesAttributesInHtml() =>
 		// language=html
 		Html.ShouldContainHtml(
-			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" /></p>"""
+			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" title="Elasticsearch" /></p>"""
 		);
 }
 
@@ -54,7 +54,7 @@ public class InlineImageWithSizingSpaceBeforeTest(ITestOutputHelper output) : In
 	public void GeneratesAttributesInHtml() =>
 		// language=html
 		Html.ShouldContainHtml(
-			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" width="50%" height="50%" /></p>"""
+			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" width="50%" height="50%" title="Elasticsearch" /></p>"""
 		);
 }
 
@@ -72,7 +72,7 @@ public class InlineImageWithSizingNoSpaceBeforeTest(ITestOutputHelper output) :
 	public void GeneratesAttributesInHtml() =>
 		// language=html
 		Html.ShouldContainHtml(
-			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" width="50%" height="50%" /></p>"""
+			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" width="50%" height="50%" title="Elasticsearch" /></p>"""
 		);
 }
 
@@ -90,11 +90,11 @@ public class InlineImageWithPixelSizingTest(ITestOutputHelper output) : InlineTe
 	public void GeneratesAttributesInHtml() =>
 		// language=html
 		Html.ShouldContainHtml(
-			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" width="250px" height="330px" /></p>"""
+			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" width="250px" height="330px" title="Elasticsearch" /></p>"""
 		);
 }
 
-// Test image sizing with title and sizing
+// Test image sizing with title and sizing — explicit title in markdown is ignored; alt text is always used as title
 public class InlineImageWithTitleAndSizingTest(ITestOutputHelper output) : InlineTest<LinkInline>(output,
 """
 ![Elasticsearch](/_static/img/observability.png "My Title =50%")
@@ -108,7 +108,7 @@ public class InlineImageWithTitleAndSizingTest(ITestOutputHelper output) : Inlin
 	public void GeneratesAttributesInHtml() =>
 		// language=html
 		Html.ShouldContainHtml(
-			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" title="My Title" width="50%" height="50%" /></p>"""
+			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" width="50%" height="50%" title="Elasticsearch" /></p>"""
 		);
 }
 
@@ -126,6 +126,6 @@ public class InlineImageWithWidthOnlyTest(ITestOutputHelper output) : InlineTest
 	public void GeneratesAttributesInHtml() =>
 		// language=html
 		Html.ShouldContainHtml(
-			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" width="250px" height="250px" /></p>"""
+			"""<p><img src="/docs/_static/img/observability.png" alt="Elasticsearch" width="250px" height="250px" title="Elasticsearch" /></p>"""
 		);
 }

tests/Elastic.Markdown.Tests/PrettyHtmlExtensions.cs

@@ -81,7 +81,7 @@ public static void ShouldContainHtml(
 		actual = actual.Trim('\n').PrettyHtml(sanitize);
 
 		var actualCompare = actual.Replace("\t", string.Empty);
-		var expectedCompare = actual.Replace("\t", string.Empty);
+		var expectedCompare = expected.Replace("\t", string.Empty);
 
 		// we compare over unindented HTML, but if that fails, we rely on the pretty HTML Contain().
 		// to throw for improved error messages

tests/Elastic.Markdown.Tests/PrettyHtmlExtensionsTests.cs

@@ -0,0 +1,27 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using AwesomeAssertions;
+using Xunit.Sdk;
+
+namespace Elastic.Markdown.Tests;
+
+public class PrettyHtmlExtensionsTests
+{
+	[Fact]
+	public void ShouldContainHtml_WhenExpectedHtmlIsMissing_Throws()
+	{
+		var actual = """
+		             <p>Rendered output</p>
+		             """;
+
+		var expected = """
+		               <strong>Missing output</strong>
+		               """;
+
+		var act = () => actual.ShouldContainHtml(expected);
+
+		act.Should().Throw<XunitException>();
+	}
+}