Add deprecation warning filter (#2546)

tests/test_deprecation.py

@@ -1,5 +1,6 @@
 import pytest
 
+from sanic import Sanic
 from sanic.log import deprecation
 
 
@@ -7,3 +8,13 @@ def test_deprecation():
     message = r"\[DEPRECATION v9\.9\] hello"
     with pytest.warns(DeprecationWarning, match=message):
         deprecation("hello", 9.9)
+
+
+@pytest.mark.parametrize(
+    "filter,expected",
+    (("default", 1), ("once", 1), ("ignore", 0)),
+)
+def test_deprecation_filter(app: Sanic, filter, expected, recwarn):
+    app.config.DEPRECATION_FILTER = filter
+    deprecation("hello", 9.9)
+    assert len(recwarn) == expected