diff --git a/.github/workflows/check_urls.yml b/.github/workflows/check_urls.yml
new file mode 100644
index 0000000..9f895ad
--- /dev/null
+++ b/.github/workflows/check_urls.yml
@@ -0,0 +1,34 @@
+name: Check URLs
+
+on: [push]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: urls-checker-code
+      uses: urlstechie/urlchecker-action@master
+      with:
+        subfolder: sphinx_runpython
+        file_types: .md,.py,.rst,.ipynb
+        print_all: false
+        timeout: 2
+        retry_count# : 2
+        # exclude_urls: https://dumps.wikimedia.org/other/pageviews/%Y/%Y-%m/pageviews-%Y%m%d-%H0000.gz,https://dumps.wikimedia.org/frwiki/latest/latest-all-titles-in-ns0.gz
+        exclude_patterns: https://dumps.wikimedia.org/
+        # force_pass : true
+
+    - name: urls-checker-docs
+      uses: urlstechie/urlchecker-action@master
+      with:
+        subfolder: _doc
+        file_types: .md,.py,.rst,.ipynb
+        print_all: false
+        timeout: 2
+        retry_count# : 2
+        # exclude_urls: https://github, ...
+        # exclude_patterns: https://github.com/...
+        # force_pass : true
diff --git a/.github/workflows/documentation.yml b/.github/workflows/documentation.yml
index 3596e4d..09562be 100644
--- a/.github/workflows/documentation.yml
+++ b/.github/workflows/documentation.yml
@@ -1,6 +1,6 @@
 name: Documentation
 
-on: [push, pull_request]
+on: [push]
 
 jobs:
   build_wheels:
@@ -26,6 +26,28 @@ jobs:
       - name: Install requirements-dev.txt
         run: python -m pip install -r requirements-dev.txt
 
+      - name: Cache pip
+        uses: actions/cache@v2
+        with:
+          path: ~/.cache/pip
+          key: ${{ runner.os }}-pip-${{ hashFiles('requirements-dev.txt') }}
+          restore-keys: |
+            ${{ runner.os }}-pip-
+            ${{ runner.os }}-
+
+      - name: Generate coverage report
+        run: |
+          pip install pytest
+          pip install pytest-cov
+          export PYTHONPATH=.
+          pytest --cov=./_unittests/ --cov-report=xml --durations=10 --ignore-glob=**LONG*.py --ignore-glob=**notebook*.py
+          export PYTHONPATH=
+
+      - name: Upload coverage reports to Codecov
+        uses: codecov/codecov-action@v3
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+
       - name: Install
         run: python -m pip install -e .
 
@@ -34,7 +56,6 @@ jobs:
           cp LICENSE* ./_doc
           cp CHANGELOGS* ./_doc
 
-
       - name: Documentation
         run: python -m sphinx ./_doc ./dist/html -n -w doc.txt
 
diff --git a/_unittests/ut__main/test_helpers.py b/_unittests/ut__main/test_helpers.py
new file mode 100644
index 0000000..7fa482e
--- /dev/null
+++ b/_unittests/ut__main/test_helpers.py
@@ -0,0 +1,13 @@
+import unittest
+from sphinx_runpython.ext_test_case import ExtTestCase
+from sphinx_runpython.conf_helper import has_dvipng, has_dvisvgm
+
+
+class TestHelpers(ExtTestCase):
+    def test_dvis(self):
+        self.assertIn(has_dvipng(), {True, False})
+        self.assertIn(has_dvisvgm(), {True, False})
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)
diff --git a/sphinx_runpython/conf_helper.py b/sphinx_runpython/conf_helper.py
new file mode 100644
index 0000000..36a27cc
--- /dev/null
+++ b/sphinx_runpython/conf_helper.py
@@ -0,0 +1,25 @@
+from .runpython import run_cmd
+
+
+def _check_cmd(cmd):
+    try:
+        stdout, _ = run_cmd(f"{cmd} --help", wait=True)
+    except FileNotFoundError:
+        return False
+    if cmd in stdout:
+        return True
+    return False
+
+
+def has_dvipng():
+    """
+    Checks `dvipng` is installed.
+    """
+    return _check_cmd("dvipng")
+
+
+def has_dvisvgm():
+    """
+    Checks `dvisvgm` is installed.
+    """
+    return _check_cmd("dvisvgm")
diff --git a/sphinx_runpython/docassert/sphinx_docassert_extension.py b/sphinx_runpython/docassert/sphinx_docassert_extension.py
index c3aded0..2e7683b 100644
--- a/sphinx_runpython/docassert/sphinx_docassert_extension.py
+++ b/sphinx_runpython/docassert/sphinx_docassert_extension.py
@@ -19,8 +19,8 @@ def check_typed_make_field(
 ):
     """
     Overwrites function
-    #L197>`_.
-    `make_field <https://github.com/sphinx-doc/sphinx/blob/master/sphinx/util/docfields.py
+    `make_field
+    <https://github.com/sphinx-doc/sphinx/blob/master/sphinx/util/docfields.py#L197>`_.
     Processes one argument of a function.
 
     :param self: from original function
@@ -116,8 +116,7 @@ def override_transform(self, other_self, node):
         """
         Transform a single field list *node*.
         Overwrite function `transform
-        <https://github.com/sphinx-doc/sphinx/blob/
-        master/sphinx/util/docfields.py#L271>`_.
+        <https://github.com/sphinx-doc/sphinx/blob/master/sphinx/util/docfields.py#L271>`_.
         It only adds extra verification and returns results from
         the replaced function.
 
diff --git a/sphinx_runpython/ext_io_helper.py b/sphinx_runpython/ext_io_helper.py
index 18a4db5..8f0c4a5 100644
--- a/sphinx_runpython/ext_io_helper.py
+++ b/sphinx_runpython/ext_io_helper.py
@@ -496,7 +496,9 @@ def download_requirejs(
             local = download(filename, to)
         except ReadUrlException as e:  # pragma: no cover
             # We implement a backup plan.
-            new_filename = "http://www.xavierdupre.fr/enseignement/setup/require.js/2.3.6/require.js"
+            new_filename = (
+                "https://requirejs.org/docs/release/2.3.6/minified/require.js"
+            )
             try:
                 local = download(new_filename, to)
             except ReadUrlException:
diff --git a/sphinx_runpython/gdot/sphinx_gdot_extension.py b/sphinx_runpython/gdot/sphinx_gdot_extension.py
index 1a3a96e..4c57604 100644
--- a/sphinx_runpython/gdot/sphinx_gdot_extension.py
+++ b/sphinx_runpython/gdot/sphinx_gdot_extension.py
@@ -282,8 +282,8 @@ def depart_gdot_node_html_svg(self, node):
 def visit_gdot_node_html(self, node):
     """
     visit collapse_node, the function switches between
-    `graphviz.py <https://github.com/sphinx-doc/sphinx/blob/
-    master/sphinx/ext/graphviz.py>`_ and the :epkg:`SVG` format.
+    `graphviz.py <https://github.com/sphinx-doc/sphinx/blob/master/sphinx/ext/graphviz.py>`_
+    and the :epkg:`SVG` format.
     """
     if node["format"].lower() == "png":
         from sphinx.ext.graphviz import html_visit_graphviz
diff --git a/sphinx_runpython/github_link.py b/sphinx_runpython/github_link.py
index 076b3c0..357e9ca 100644
--- a/sphinx_runpython/github_link.py
+++ b/sphinx_runpython/github_link.py
@@ -23,16 +23,6 @@ def _linkcode_resolve(domain, info, package, url_fmt, revision):
     Determine a link to online source for a class/method/function
 
     This is called by sphinx.ext.linkcode
-
-    An example with a long-untouched module that everyone has:
-
-    >>> _linkcode_resolve('py', {'module': 'tty',
-    ...                          'fullname': 'setraw'},
-    ...                   package='tty',
-    ...                   url_fmt='http://hg.python.org/cpython/file/'
-    ...                           '{revision}/Lib/{package}/{path}#L{lineno}',
-    ...                   revision='xxxx')
-    'http://hg.python.org/cpython/file/xxxx/Lib/tty/tty.py#L18'
     """
 
     if revision is None:
diff --git a/sphinx_runpython/runpython/run_cmd.py b/sphinx_runpython/runpython/run_cmd.py
index 4d511ff..5176b0e 100644
--- a/sphinx_runpython/runpython/run_cmd.py
+++ b/sphinx_runpython/runpython/run_cmd.py
@@ -119,7 +119,7 @@ def skip_run_cmd(
 def run_cmd(
     cmd,
     sin="",
-    shell=sys.platform.startswith("win"),
+    shell=None,
     wait=False,
     log_error=True,
     stop_running_if=None,
@@ -184,6 +184,8 @@ def run_cmd(
     ``__exit__`` should be called if wait if False.
     Parameter *prefix_log* was added.
     """
+    if shell is None:
+        shell = sys.platform.startswith("win")
     if prefix_log is None:
         prefix_log = ""
     if logf is not None: