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How to Mock CLI Output in Typer with unittest.mock

Mock and capture Typer CLI output using unittest.mock.patch and io.StringIO for testing command-line applications.

typer cli testing
Python 
import typer
from unittest.mock import patch
import io

app = typer.Typer()

@app.command()
def greet(name: str, age: int = 18, uppercase: bool = False):
    """Greet a person with optional formatting."""
    message = f"Hello {name}, age {age}"
    if uppercase:
        message = message.upper()
    typer.echo(messag…
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