diff --git a/tests/notebooks/mirror/ipynb_to_md/Notebook with metadata and long cells.md b/tests/notebooks/mirror/ipynb_to_md/Notebook with metadata and long cells.md
index de273fc00..73325a3fa 100644
--- a/tests/notebooks/mirror/ipynb_to_md/Notebook with metadata and long cells.md	
+++ b/tests/notebooks/mirror/ipynb_to_md/Notebook with metadata and long cells.md	
@@ -35,11 +35,11 @@ After that cell we'll have a code cell
 
 Followed by a raw cell
 
-```
+<!-- #raw -->
 This is 
 the content
 of the raw cell
-```
+<!-- #endraw -->
 
 # Part two - cell metadata
 
@@ -51,6 +51,6 @@ This is a markdown cell with cell metadata `{"key": "value"}`
 """This is a code cell with metadata `{"tags":["parameters"], ".class":null}`"""
 ```
 
-```key="value"
+<!-- #raw {"key": "value"} -->
 This is a raw cell with cell metadata `{"key": "value"}`
-```
+<!-- #endraw -->
diff --git a/tests/notebooks/mirror/ipynb_to_md/The flavors of raw cells.md b/tests/notebooks/mirror/ipynb_to_md/The flavors of raw cells.md
index 137aa8ce4..a22bad50c 100644
--- a/tests/notebooks/mirror/ipynb_to_md/The flavors of raw cells.md	
+++ b/tests/notebooks/mirror/ipynb_to_md/The flavors of raw cells.md	
@@ -6,26 +6,26 @@ jupyter:
     name: python3
 ---
 
-```raw_mimetype="text/latex"
+<!-- #raw {"raw_mimetype": "text/latex"} -->
 $1+1$
-```
+<!-- #endraw -->
 
-```raw_mimetype="text/restructuredtext"
+<!-- #raw {"raw_mimetype": "text/restructuredtext"} -->
 :math:`1+1`
-```
+<!-- #endraw -->
 
-```raw_mimetype="text/html"
+<!-- #raw {"raw_mimetype": "text/html"} -->
 <b>Bold text<b>
-```
+<!-- #endraw -->
 
-```raw_mimetype="text/markdown"
+<!-- #raw {"raw_mimetype": "text/markdown"} -->
 **Bold text**
-```
+<!-- #endraw -->
 
-```raw_mimetype="text/x-python"
+<!-- #raw {"raw_mimetype": "text/x-python"} -->
 1 + 1
-```
+<!-- #endraw -->
 
-```
+<!-- #raw -->
 Not formatted
-```
+<!-- #endraw -->
diff --git a/tests/notebooks/mirror/ipynb_to_md/jupyter_with_raw_cell_in_body.md b/tests/notebooks/mirror/ipynb_to_md/jupyter_with_raw_cell_in_body.md
index 1f3953bbd..f829ab214 100644
--- a/tests/notebooks/mirror/ipynb_to_md/jupyter_with_raw_cell_in_body.md
+++ b/tests/notebooks/mirror/ipynb_to_md/jupyter_with_raw_cell_in_body.md
@@ -10,8 +10,8 @@ jupyter:
 1+2+3
 ```
 
-```
+<!-- #raw -->
 This is a raw cell
-```
+<!-- #endraw -->
 
 This is a markdown cell
diff --git a/tests/notebooks/mirror/md_to_ipynb/jupytext_markdown.ipynb b/tests/notebooks/mirror/md_to_ipynb/jupytext_markdown.ipynb
index a73c2ad01..329fe9f8a 100644
--- a/tests/notebooks/mirror/md_to_ipynb/jupytext_markdown.ipynb
+++ b/tests/notebooks/mirror/md_to_ipynb/jupytext_markdown.ipynb
@@ -47,10 +47,12 @@
    ]
   },
   {
-   "cell_type": "raw",
+   "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "THIS IS A RAW CELL"
+    "```\n",
+    "THIS IS A RAW CELL\n",
+    "```"
    ]
   },
   {
diff --git a/tests/notebooks/mirror/md_to_ipynb/plain_markdown.ipynb b/tests/notebooks/mirror/md_to_ipynb/plain_markdown.ipynb
new file mode 100644
index 000000000..2ba73714a
--- /dev/null
+++ b/tests/notebooks/mirror/md_to_ipynb/plain_markdown.ipynb
@@ -0,0 +1,95 @@
+{
+ "cells": [
+  {
+   "cell_type": "raw",
+   "metadata": {},
+   "source": [
+    "---\n",
+    "title: A sample document\n",
+    "---"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "This document is a plain Markdown document that was not created from a notebook.\n",
+    "We use this document to test that inputing a Markdown file into Jupytext, and then converting the\n",
+    "resulting notebook to a Markdown file using nbconvert, is the identity\n",
+    "\n",
+    "Another paragraph\n",
+    "\n",
+    "# A header\n",
+    "\n",
+    "Indented code\n",
+    "\n",
+    "    def f(x):\n",
+    "        return 1\n",
+    "\n",
+    "\n",
+    "    def h(x):\n",
+    "        return f(x)+2\n",
+    "\n",
+    "\n",
+    "A Python code snippet"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "\"\"\"This code cell starts with ` ```python`\"\"\"\n",
+    "1 + 1"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {
+    "lines_to_next_cell": 0
+   },
+   "source": [
+    "Code snippet without an explicit language"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "```\n",
+    "echo 'Hello world'\n",
+    "```"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Markdown comments\n",
+    "<!-- #comment -->\n",
+    "\n",
+    "VS Code region markers"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "This Markdown cell has two consecutive blank lines\n",
+    "\n",
+    "\n",
+    "And continues here"
+   ]
+  }
+ ],
+ "metadata": {
+  "jupytext": {
+   "cell_metadata_filter": "-all",
+   "main_language": "python",
+   "notebook_metadata_filter": "-all"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}