Add unit test for issue #10436: YAML delimiter detection

Tests the fix for mid-document YAML blocks that are incorrectly parsed
when the closing delimiter is followed by a blank line.

Three test cases:
1. Mid-document YAML with blank line - verifies the bug fix
2. Multiple mid-document YAML blocks - tests edge cases
3. Slide separators not treated as YAML - regression test for #8998

The tests verify that quartoMdToJupyter() correctly creates raw cells
for mid-document YAML blocks without spurious blank lines after the
opening delimiter.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

tests/unit/core/jupyter-yaml-delimiter.test.ts

@@ -0,0 +1,170 @@
+/*
+* jupyter-yaml-delimiter.test.ts
+*
+* Test for issue #10436: YAML closing delimiter detection with blank lines
+*
+* Copyright (C) 2020-2026 Posit Software, PBC
+*/
+import { assertEquals, assert } from "testing/asserts";
+import { quartoMdToJupyter } from "../../../src/core/jupyter/jupyter.ts";
+import { unitTest } from "../../test.ts";
+
+unitTest("quartoMdToJupyter: mid-document YAML with blank line", async () => {
+  const markdown = `---
+title: "Test Document"
+---
+
+## Section 1
+
+Some intro text.
+
+---
+jupyter: python3
+title: "Mid-Document Block"
+---
+
+More content after YAML.
+
+\`\`\`{python}
+2 + 2
+\`\`\`
+`;
+
+  const notebook = await quartoMdToJupyter(markdown, false);
+
+  // Verify we have the correct number of cells
+  assertEquals(notebook.cells.length, 5);
+
+  // Cell 0: raw cell with document frontmatter
+  assertEquals(notebook.cells[0].cell_type, "raw");
+  const cell0Source = Array.isArray(notebook.cells[0].source)
+    ? notebook.cells[0].source.join("")
+    : notebook.cells[0].source;
+  assert(cell0Source.includes('title: "Test Document"'));
+
+  // Cell 1: markdown cell with intro
+  assertEquals(notebook.cells[1].cell_type, "markdown");
+  const cell1Source = Array.isArray(notebook.cells[1].source)
+    ? notebook.cells[1].source.join("")
+    : notebook.cells[1].source;
+  assert(cell1Source.includes("## Section 1"));
+  assert(cell1Source.includes("Some intro text."));
+
+  // Cell 2: raw cell with mid-document YAML (THE KEY TEST)
+  assertEquals(notebook.cells[2].cell_type, "raw");
+  const cell2Source = Array.isArray(notebook.cells[2].source)
+    ? notebook.cells[2].source.join("")
+    : notebook.cells[2].source;
+
+  // CRITICAL: Verify YAML delimiters are correct
+  assert(cell2Source.startsWith("---\n"), "Mid-document YAML should start with ---\\n");
+  assert(cell2Source.includes("jupyter: python3"), "Should contain YAML content");
+  assert(cell2Source.includes('title: "Mid-Document Block"'), "Should contain YAML content");
+  assert(cell2Source.endsWith("---"), "Mid-document YAML should end with ---");
+
+  // CRITICAL: Verify NO blank line after opening ---
+  assert(!cell2Source.match(/^---\n\njupyter:/), "Should NOT have blank line after opening ---");
+
+  // Cell 3: markdown cell with content after YAML
+  assertEquals(notebook.cells[3].cell_type, "markdown");
+  const cell3Source = Array.isArray(notebook.cells[3].source)
+    ? notebook.cells[3].source.join("")
+    : notebook.cells[3].source;
+  assert(cell3Source.includes("More content after YAML."));
+
+  // Cell 4: code cell
+  assertEquals(notebook.cells[4].cell_type, "code");
+  const cell4Source = Array.isArray(notebook.cells[4].source)
+    ? notebook.cells[4].source.join("")
+    : notebook.cells[4].source;
+  assert(cell4Source.includes("2 + 2"));
+});
+
+unitTest("quartoMdToJupyter: multiple mid-document YAML blocks", async () => {
+  const markdown = `---
+title: "Main"
+---
+
+## First Section
+
+---
+config1: value1
+---
+
+Content between.
+
+---
+config2: value2
+---
+
+\`\`\`{python}
+print("test")
+\`\`\`
+`;
+
+  const notebook = await quartoMdToJupyter(markdown, false);
+
+  // Should have 6 cells: frontmatter, intro, yaml1, content, yaml2, code
+  assertEquals(notebook.cells.length, 6);
+
+  // Verify cell types
+  assertEquals(notebook.cells[0].cell_type, "raw");  // frontmatter
+  assertEquals(notebook.cells[1].cell_type, "markdown");  // "## First Section"
+  assertEquals(notebook.cells[2].cell_type, "raw");  // first YAML block
+  assertEquals(notebook.cells[3].cell_type, "markdown");  // "Content between."
+  assertEquals(notebook.cells[4].cell_type, "raw");  // second YAML block
+  assertEquals(notebook.cells[5].cell_type, "code");  // python code
+
+  // Verify both YAML blocks have correct structure
+  const yaml1 = Array.isArray(notebook.cells[2].source)
+    ? notebook.cells[2].source.join("")
+    : notebook.cells[2].source;
+  assert(yaml1.includes("config1: value1"));
+  assert(!yaml1.match(/^---\n\nconfig1/));  // No blank line
+
+  const yaml2 = Array.isArray(notebook.cells[4].source)
+    ? notebook.cells[4].source.join("")
+    : notebook.cells[4].source;
+  assert(yaml2.includes("config2: value2"));
+  assert(!yaml2.match(/^---\n\nconfig2/));  // No blank line
+});
+
+unitTest("quartoMdToJupyter: slide separators not treated as YAML", async () => {
+  const markdown = `---
+title: "Presentation"
+format: revealjs
+---
+
+# Slide 1
+
+Content on first slide.
+
+---
+
+# Slide 2
+
+Content on second slide.
+
+\`\`\`{python}
+x = 1
+\`\`\`
+`;
+
+  const notebook = await quartoMdToJupyter(markdown, false);
+
+  // The --- between slides should NOT create a YAML cell
+  // Should have: frontmatter + markdown (all slides together) + code
+  assertEquals(notebook.cells.length, 3);
+
+  assertEquals(notebook.cells[0].cell_type, "raw");  // frontmatter
+  assertEquals(notebook.cells[1].cell_type, "markdown");  // all slide content
+  assertEquals(notebook.cells[2].cell_type, "code");  // python
+
+  // Verify the markdown cell contains the slide separator
+  const markdownSource = Array.isArray(notebook.cells[1].source)
+    ? notebook.cells[1].source.join("")
+    : notebook.cells[1].source;
+  assert(markdownSource.includes("---"), "Slide separator should be in markdown");
+  assert(markdownSource.includes("# Slide 1"));
+  assert(markdownSource.includes("# Slide 2"));
+});