Add tests

Author: pfmoore

tests/functional/test_python_option.py

@@ -0,0 +1,33 @@
+import json
+import os
+from pathlib import Path
+from venv import EnvBuilder
+
+from tests.lib import PipTestEnvironment, TestData
+
+
+def test_python_interpreter(
+    script: PipTestEnvironment,
+    tmpdir: Path,
+    shared_data: TestData,
+) -> None:
+    env_path = os.fsdecode(tmpdir / "venv")
+    env = EnvBuilder(with_pip=False)
+    env.create(env_path)
+
+    result = script.pip("--python", env_path, "list", "--format=json")
+    assert json.loads(result.stdout) == []
+    script.pip(
+        "--python",
+        env_path,
+        "install",
+        "-f",
+        shared_data.find_links,
+        "--no-index",
+        "simplewheel==1.0",
+    )
+    result = script.pip("--python", env_path, "list", "--format=json")
+    assert json.loads(result.stdout) == [{"name": "simplewheel", "version": "1.0"}]
+    script.pip("--python", env_path, "uninstall", "simplewheel", "--yes")
+    result = script.pip("--python", env_path, "list", "--format=json")
+    assert json.loads(result.stdout) == []

tests/unit/test_cmdoptions.py

@@ -1,8 +1,12 @@
+import os
+from pathlib import Path
 from typing import Optional, Tuple
+from venv import EnvBuilder
 
 import pytest
 
 from pip._internal.cli.cmdoptions import _convert_python_version
+from pip._internal.cli.main_parser import identify_python_interpreter
 
 
 @pytest.mark.parametrize(
@@ -29,3 +33,30 @@ def test_convert_python_version(
 ) -> None:
     actual = _convert_python_version(value)
     assert actual == expected, f"actual: {actual!r}"
+
+
+def test_identify_python_interpreter_py(monkeypatch: pytest.MonkeyPatch) -> None:
+    def which(cmd: str) -> str:
+        assert cmd == "py" or cmd == "python"
+        return "dummy_value"
+
+    monkeypatch.setattr("shutil.which", which)
+    assert identify_python_interpreter("py") == "dummy_value"
+    assert identify_python_interpreter("python") == "dummy_value"
+
+
+def test_identify_python_interpreter_venv(tmpdir: Path) -> None:
+    env_path = tmpdir / "venv"
+    env = EnvBuilder(with_pip=False)
+    env.create(env_path)
+
+    # Passing a virtual environment returns the Python executable
+    interp = identify_python_interpreter(os.fsdecode(env_path))
+    assert interp is not None
+    assert Path(interp).exists()
+
+    # Passing an executable returns it
+    assert identify_python_interpreter(interp) == interp
+
+    # Passing a non-existent file returns None
+    assert identify_python_interpreter(str(tmpdir / "nonexistent")) is None