Tests: ensure default values appear in help output

docs/tutorial/commands/help.md

@@ -29,6 +29,36 @@ Commands:
   delete-all  Delete ALL users in the database.
   init        Initialize the users database.
 
+### How Typer generates `--help` output
+
+Typer builds command-line interfaces on top of
+[Click](https://click.palletsprojects.com/), which means all `--help`
+output is ultimately generated by Click.
+
+Typer automatically:
+
+- Converts function names into command names
+- Converts function parameters into CLI options and arguments
+- Uses type hints and default values to generate help text
+
+For example:
+
+```python
+import typer
+
+app = typer.Typer()
+
+@app.command()
+def greet(name: str, formal: bool = False):
+    """
+    Say hello to a user.
+    """
+    if formal:
+        typer.echo(f"Hello {name}.")
+    else:
+        typer.echo(f"Hi {name}!")
+
+
 // Now the commands have inline help 🎉
 
 // Check the help for create

tests/test_help_defaults.py

@@ -0,0 +1,18 @@
+import typer
+from typer.testing import CliRunner
+
+runner = CliRunner()
+
+
+def test_default_value_in_help():
+    app = typer.Typer()
+
+    @app.command()
+    def hello(name: str = "World"):
+        typer.echo(f"Hello {name}")
+
+    result = runner.invoke(app, ["--help"])
+
+    assert result.exit_code == 0
+    assert "World" in result.output
+