Add very simple tests to ensure feature is enabled

tests/functional/test_truststore.py

@@ -0,0 +1,61 @@
+import sys
+from typing import Any, Callable
+
+import pytest
+
+from tests.lib import PipTestEnvironment, TestPipResult
+
+PipRunner = Callable[..., TestPipResult]
+
+
+@pytest.fixture()
+def pip(script: PipTestEnvironment) -> PipRunner:
+    def pip(*args: str, **kwargs: Any) -> TestPipResult:
+        return script.pip(*args, "--use-feature=truststore", **kwargs)
+
+    return pip
+
+
+@pytest.mark.skipif(sys.version_info >= (3, 10), reason="3.10 can run truststore")
+def test_truststore_error_on_old_python(pip: PipRunner) -> None:
+    result = pip(
+        "install",
+        "--no-index",
+        "does-not-matter",
+        expect_error=True,
+    )
+    assert "The truststore feature is only available for Python 3.10+" in result.stderr
+
+
+@pytest.mark.skipif(sys.version_info < (3, 10), reason="3.10+ required for truststore")
+def test_truststore_error_without_preinstalled(pip: PipRunner) -> None:
+    result = pip(
+        "install",
+        "--no-index",
+        "does-not-matter",
+        expect_error=True,
+    )
+    assert (
+        "To use the truststore feature, 'truststore' must be installed into "
+        "pip's current environment."
+    ) in result.stderr
+
+
+@pytest.mark.skipif(sys.version_info < (3, 10), reason="3.10+ required for truststore")
+@pytest.mark.network
+@pytest.mark.parametrize(
+    "package",
+    [
+        "INITools",
+        "https://github.com/pypa/pip-test-package/archive/refs/heads/master.zip",
+    ],
+    ids=["PyPI", "GitHub"],
+)
+def test_trustore_can_install(
+    script: PipTestEnvironment,
+    pip: PipRunner,
+    package: str,
+) -> None:
+    script.pip("install", "truststore")
+    result = pip("install", package)
+    assert "Successfully installed" in result.stdout