serve per-instance static files at custom-static/

tests/functional_tests.py

@@ -218,3 +218,23 @@ def test_extra_footer_per_page(client):
     assert b'<div class="extra-footer">' not in response.data
     response = client.get('/index-but-with-footer')
     assert b'<div class="extra-footer"><i>ooo <a href="a">a</a></i>' in response.data
+
+
+def test_serving_static_files(client):
+    """Test the usage of send_from_directory to serve extra static files."""
+    response = client.get('/custom-static/css/warm.css')
+    assert response.status_code == 200
+
+    # can't serve directories, just files
+    response = client.get('/custom-static/')
+    assert response.status_code == 404
+    response = client.get('/custom-static/css/')
+    assert response.status_code == 404
+    response = client.get('/custom-static/css')
+    assert response.status_code == 404
+
+    # can't serve files that don't exist or bad paths
+    response = client.get('/custom-static/css/cold.css')
+    assert response.status_code == 404
+    response = client.get('/custom-static/css/../../unreachable.md')
+    assert response.status_code == 404

tests/instance/custom-static/css/warm.css

@@ -0,0 +1,3 @@
+* {
+    color: red;
+}