Test callable environments formatting

If the environment has an escaped variable (so, a string), the server should start without failing to format it.

Author: diocas

tests/resources/jupyter_server_config.py

@@ -42,6 +42,10 @@ def cats_only(response, path):
         response.code = 403
         response.body = b"dogs not allowed"
 
+def my_env():
+    return {
+            "MYVAR": "String with escaped {{var}}"
+        }
 
 c.ServerProxy.servers = {
     "python-http": {
@@ -65,6 +69,10 @@ def cats_only(response, path):
         "command": [sys.executable, "./tests/resources/httpinfo.py", "--port={port}"],
         "mappath": mappathf,
     },
+    "python-http-callable-env": {
+        "command": [sys.executable, "./tests/resources/httpinfo.py", "--port={port}"],
+        "environment": my_env,
+    },
     "python-websocket": {
         "command": [sys.executable, "./tests/resources/websocket.py", "--port={port}"],
         "request_headers_override": {

tests/test_proxies.py

@@ -408,3 +408,9 @@ def test_bad_server_proxy_url(
     if status >= 400:
         # request should not have been proxied
         assert "X-ProxyContextPath" not in r.headers
+
+
+def test_callable_environment_formatting(a_server_port_and_token: Tuple[int, str]) -> None:
+    PORT, TOKEN = a_server_port_and_token
+    r = request_get(PORT, "/python-http-callable-env/test", TOKEN)
+    assert r.code == 200