clan join: test create vm for clan join

This adds a vm create test for the `clan join` scenario where:
  - there is no local clan to write changes to
  - a machine from a remote flake needs to be built and run
  - no users and no secrets need to be or can be managed (no flake to write files to)

pkgs/clan-cli/tests/fixtures_flakes.py

@@ -0,0 +1,90 @@
+import fileinput
+import shutil
+import tempfile
+from pathlib import Path
+from typing import Iterator
+
+import pytest
+from root import CLAN_CORE
+
+from clan_cli.dirs import nixpkgs_source
+
+
+# substitutes string sin a file.
+# This can be used on the flake.nix or default.nix of a machine
+def substitute(
+    file: Path,
+    clan_core_flake: Path | None = None,
+    flake: Path = Path(__file__).parent,
+) -> None:
+    sops_key = str(flake.joinpath("sops.key"))
+    for line in fileinput.input(file, inplace=True):
+        line = line.replace("__NIXPKGS__", str(nixpkgs_source()))
+        if clan_core_flake:
+            line = line.replace("__CLAN_CORE__", str(clan_core_flake))
+        line = line.replace("__CLAN_SOPS_KEY_PATH__", sops_key)
+        line = line.replace("__CLAN_SOPS_KEY_DIR__", str(flake))
+        print(line, end="")
+
+
+def create_flake(
+    monkeypatch: pytest.MonkeyPatch,
+    name: str,
+    clan_core_flake: Path | None = None,
+    machines: list[str] = [],
+    remote: bool = False,
+) -> Iterator[Path]:
+    """
+    Creates a flake with the given name and machines.
+    The machine names map to the machines in ./test_machines
+    """
+    template = Path(__file__).parent / name
+    # copy the template to a new temporary location
+    with tempfile.TemporaryDirectory() as tmpdir_:
+        home = Path(tmpdir_)
+        flake = home / name
+        shutil.copytree(template, flake)
+        # lookup the requested machines in ./test_machines and include them
+        if machines:
+            (flake / "machines").mkdir(parents=True, exist_ok=True)
+        for machine_name in machines:
+            machine_path = Path(__file__).parent / "machines" / machine_name
+            shutil.copytree(machine_path, flake / "machines" / machine_name)
+            substitute(flake / "machines" / machine_name / "default.nix", flake)
+        # in the flake.nix file replace the string __CLAN_URL__ with the the clan flake
+        # provided by get_test_flake_toplevel
+        flake_nix = flake / "flake.nix"
+        # this is where we would install the sops key to, when updating
+        substitute(flake_nix, clan_core_flake, flake)
+        if remote:
+            with tempfile.TemporaryDirectory() as workdir:
+                monkeypatch.chdir(workdir)
+                monkeypatch.setenv("HOME", str(home))
+                yield flake
+        else:
+            monkeypatch.chdir(flake)
+            monkeypatch.setenv("HOME", str(home))
+            yield flake
+
+
+@pytest.fixture
+def test_flake(monkeypatch: pytest.MonkeyPatch) -> Iterator[Path]:
+    yield from create_flake(monkeypatch, "test_flake")
+
+
+@pytest.fixture
+def test_flake_with_core(monkeypatch: pytest.MonkeyPatch) -> Iterator[Path]:
+    if not (CLAN_CORE / "flake.nix").exists():
+        raise Exception(
+            "clan-core flake not found. This test requires the clan-core flake to be present"
+        )
+    yield from create_flake(monkeypatch, "test_flake_with_core", CLAN_CORE)
+
+
+@pytest.fixture
+def test_flake_with_core_and_pass(monkeypatch: pytest.MonkeyPatch) -> Iterator[Path]:
+    if not (CLAN_CORE / "flake.nix").exists():
+        raise Exception(
+            "clan-core flake not found. This test requires the clan-core flake to be present"
+        )
+    yield from create_flake(monkeypatch, "test_flake_with_core_and_pass", CLAN_CORE)