Add test for deprecation warning

tests/test_deprecation.py

@@ -0,0 +1,27 @@
+from typing import Optional
+
+import pytest
+import typer
+from typer.testing import CliRunner
+
+runner = CliRunner()
+
+
+def test_deprecation():
+    app = typer.Typer()
+
+    def add_command():
+        @app.command()
+        def cmd(
+            opt: Optional[float] = typer.Option(
+                3.14,
+                is_flag=True,
+                flag_value="42",
+                help="Some wonderful number",
+            ),
+        ): ...  # pragma: no cover
+
+    with pytest.warns(
+        match="The 'is_flag' and 'flag_value' parameters are not supported by Typer"
+    ):
+        add_command()

typer/models.py

@@ -384,7 +384,7 @@ def __init__(
 
             warnings.warn(
                 "The 'is_flag' and 'flag_value' parameters are not supported by Typer "
-                " and will be removed entirely in a future release.",
+                "and will be removed entirely in a future release.",
                 DeprecationWarning,
                 stacklevel=2,
             )