Add code snippets to long-form stories.

test_code_snippets.py

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+import unittest
+
+import app as application
+
+
+class CodeSnippetTestCase(unittest.TestCase):
+    def test_fenced_code_is_parsed_with_its_language(self):
+        blocks = application.article_blocks('Intro\n```python\nprint("hi")\n```\nEnd', [])
+
+        self.assertEqual(blocks[0], ("text", "Intro\n"))
+        self.assertEqual(blocks[1], ("code", {"language": "python", "content": 'print("hi")'}))
+        self.assertEqual(blocks[2], ("text", "\nEnd"))
+
+    def test_code_fence_keeps_image_marker_as_literal_code(self):
+        image = {"filename": "step.webp"}
+        blocks = application.article_blocks("```\n[[image:1]]\n```\n[[image:1]]", [image])
+
+        self.assertEqual(blocks[0], ("code", {"language": "text", "content": "[[image:1]]"}))
+        self.assertEqual(blocks[1], ("text", "\n"))
+        self.assertEqual(blocks[2], ("image", image))
+
+    def test_unterminated_fence_is_plain_text(self):
+        body = "```python\nprint('not closed')"
+
+        self.assertEqual(application.article_blocks(body, []), [("text", body)])
+
+
+if __name__ == "__main__":
+    unittest.main()