Add test for auto_reload (coverage not working unfortunately).

tests/test_auto_reload.py

@@ -0,0 +1,46 @@
+import os
+import subprocess
+import secrets
+import sys
+
+from tempfile import TemporaryDirectory
+from textwrap import dedent
+
+import pytest
+
+def write_app(filename, **runargs):
+    text = secrets.token_urlsafe()
+    with open(filename, "w") as f:
+        f.write(dedent(f"""\
+            from sanic import Sanic
+            from sanic.response import text
+
+            app = Sanic(__name__)
+
+            @app.listener("after_server_start")
+            def complete(*args):
+                print("complete", {text!r})
+
+            kwargs = {runargs!r}
+            app.run(port=42101, **kwargs)
+            """
+        ))
+    return text
+
+@pytest.mark.parametrize("runargs", [
+    dict(auto_reload=True),
+    dict(debug=True),
+])
+async def test_reloader_live(runargs):
+    with TemporaryDirectory() as tmpdir:
+        filename = os.path.join(tmpdir, "reloaderapp.py")
+        text = write_app(filename, **runargs)
+        with subprocess.Popen([sys.executable, filename], stdout=subprocess.PIPE) as proc:
+            line = (l.decode() for l in proc.stdout if l.startswith(b"complete"))
+            try:
+                assert next(line) == f"complete {text}\n"
+                # Edit source code and try again
+                text = write_app(filename)
+                assert next(line) == f"complete {text}\n"
+            finally:
+                proc.terminate()