$ uv init --package demo-stdin-stdout-pytest
Initialized project `demo-stdin-stdout-pytest` at `/home/cpitcher/working/python/examples/demo-stdin-stdout-pytest`

$ cd demo-stdin-stdout-pytest/

$ uv add --dev pytest
Using CPython 3.14.0
Creating virtual environment at: .venv
Resolved 7 packages in 172ms
      Built demo-stdin-stdout-pytest @ file:///home/cpitcher/working/python/exampl
Prepared 1 package in 5ms
Installed 6 packages in 14ms
 + demo-stdin-stdout-pytest==0.1.0 (from file:///home/cpitcher/working/python/examples/demo-stdin-stdout-pytest)
 + iniconfig==2.3.0
 + packaging==25.0
 + pluggy==1.6.0
 + pygments==2.19.2
 + pytest==8.4.2

$ git add .gitignore .python-version README.md pyproject.toml src/ uv.lock 

$ git commit -m "Initial commit"
[master (root-commit) ccfa99c] Initial commit
 6 files changed, 114 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 .python-version
 create mode 100644 README.md
 create mode 100644 pyproject.toml
 create mode 100644 src/demo_stdin_stdout_pytest/__init__.py
 create mode 100644 uv.lock

• update src/demo_pytest/__init__.py{.verbatim} to:

  import json
  from pathlib import Path
  
  def prompt_for_user_data() -> dict:
      name = input("Enter your name: ")
      age = input("Enter your age: ")
      city = input("Enter your city: ")
      return {
          "name": name,
          "age": age,
          "city": city
      }
  
  def save_user_data(data: dict, filepath: Path) -> None:
      with open(filepath, "w") as f:
          json.dump(data, f)
  
  def main() -> None:
      data = prompt_for_user_data()
      save_user_data(data, Path.cwd() / "data.json")
      print(f"Thanks {data['name']}")
  
  if __name__ == "__main__":
      main()

• run the main{.verbatim} function in src/demo_pytest/__init__.py{.verbatim}:

  $ uv run demo-stdin-stdout-pytest
  Enter your name: alice
  Enter your age: 20
  Enter your city: chicago
  Thanks alice
  

• examine the JSON output:

  $ cat data.json 
  {"name": "alice", "age": "20", "city": "chicago"}
  
  $ jq . data.json 
  {
    "name": "alice",
    "age": "20",
    "city": "chicago"
  }
  

• add and commit the implementation

  $ git add src/demo_stdin_stdout_pytest/__init__.py 
  $ echo data.json >> .gitignore
  $ git add .gitignore 
  
  $ git commit -m "Added implementation"
  [master 38acb3f] Added implementation
   2 files changed, 24 insertions(+), 1 deletion(-)
  

• create Python test code in tests/test_user_data.py{.verbatim}:

  from demo_stdin_stdout_pytest import prompt_for_user_data, save_user_data, print_confirmation
  import json
  from pathlib import Path
  
  def test_prompt_for_user_data(monkeypatch):
      inputs = iter(["Alice", "20", "Chicago"])
      monkeypatch.setattr('builtins.input', lambda _: next(inputs))
  
      data = prompt_for_user_data()
      assert data == {
          "name": "Alice",
          "age": "20",
          "city": "Chicago"
      }
  
  def test_save_user_data(tmp_path):
      data = {
          "name": "Bob",
          "age": "25",
          "city": "New York"
      }
      filepath = tmp_path / "user_data.json"
      save_user_data(data, filepath)
  
      with open(filepath, "r") as f:
          loaded_data = json.load(f)
  
      assert loaded_data == data
  
  def test_print_confirmation(capsys):
      print_confirmation("Charlie")
      captured = capsys.readouterr()
      assert captured.out.strip() == "Thanks Charlie"

• run pytest:

  $ uv run pytest
  ============================ test session starts =============================
  platform linux -- Python 3.14.0, pytest-8.4.2, pluggy-1.6.0
  rootdir: /home/cpitcher/working/python/examples/demo-stdin-stdout-pytest
  configfile: pyproject.toml
  collected 3 items                                                            
  
  tests/test_user_data.py ...                                            [100%]
  
  ============================= 3 passed in 0.01s ==============================
  

• add and commit the tests:

  $ git add tests/test_user_data.py 
  
  $ git commit -m "Added tests"
  [master 9f43ca7] Added tests
   1 file changed, 33 insertions(+)
   create mode 100644 tests/test_user_data.py