Add packse scenario tests (#746)

Adds tests using packse test scenarios! Uses `test.pypi.org` as a
backing index.

Tests are generated by a simple Python script. Requires
https://github.com/zanieb/packse/pull/49.

This opens us to a slight attack surface, as we cannot force use of
`test.pypi.org` only and someone could register these package names on
the real `pypi.org` index with malicious content. I could publish these
packages there too.

scripts/scenarios/generate.py

@@ -0,0 +1,86 @@
+"""
+Generates snapshot test cases from packse scenarios.
+
+Usage:
+    $ python scripts/scenarios/generate.py > crates/puffin-cli/tests/pip_install_scenarios.rs
+"""
+try:
+    import packse
+except ImportError:
+    print("packse must be installed")
+    exit(1)
+
+import sys
+import subprocess
+import json
+
+
+TEMPLATE = """
+/// {{ name }}
+///
+/// {{ description }}
+#[test]
+fn {{ test_name }}() -> Result<()> {
+    let temp_dir = assert_fs::TempDir::new()?;
+    let cache_dir = assert_fs::TempDir::new()?;
+    let venv = create_venv_py312(&temp_dir, &cache_dir);
+
+    insta::with_settings!({
+        filters => INSTA_FILTERS.to_vec()
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .arg("pip-install")
+            .arg("{{ prefix }}")
+            .arg("--extra-index-url")
+            .arg("https://test.pypi.org/simple")
+            .arg("--cache-dir")
+            .arg(cache_dir.path())
+            .env("VIRTUAL_ENV", venv.as_os_str())
+            .current_dir(&temp_dir), @r###"<snapshot>
+        "###);
+    });
+
+    Ok(())
+}
+"""
+
+PRELUDE = """
+#![cfg(all(feature = "python", feature = "pypi"))]
+/// Generated by `{{ generated_by }}`
+
+use std::process::Command;
+
+use anyhow::Result;
+use insta_cmd::_macro_support::insta;
+use insta_cmd::{assert_cmd_snapshot, get_cargo_bin};
+
+use common::{create_venv_py312, BIN_NAME, INSTA_FILTERS};
+
+mod common;
+"""
+
+scenarios = json.loads(
+    subprocess.check_output(
+        [
+            "packse",
+            "inspect",
+            str(packse.__development_base_path__ / "scenarios"),
+        ],
+    )
+)["scenarios"]
+
+output = PRELUDE.lstrip().replace("{{ generated_by }}", " ".join(sys.argv))
+
+for scenario in scenarios:
+    # Skip the example scenario file
+    if scenario["name"] == "example":
+        continue
+
+    output += (
+        TEMPLATE.replace("{{ name }}", scenario["name"])
+        .replace("{{ test_name }}", scenario["name"].replace("-", "_"))
+        .replace("{{ description }}", scenario["description"])
+        .replace("{{ prefix }}", scenario["prefix"])
+    )
+
+print(output)