2 files changed, 121 insertions, 0 deletions
diff --git a/tests/functional2/testlib/__init__.py b/tests/functional2/testlib/__init__.py
new file mode 100644
index 000000000..e69de29bb
--- /dev/null
+++ b/tests/functional2/testlib/__init__.py
diff --git a/tests/functional2/testlib/fixtures.py b/tests/functional2/testlib/fixtures.py
new file mode 100644
index 000000000..bbaaae51d
--- /dev/null
+++ b/tests/functional2/testlib/fixtures.py
@@ -0,0 +1,121 @@
+import os
+import json
+import subprocess
+from typing import Any
+from pathlib import Path
+import dataclasses
+
+
+@dataclasses.dataclass
+class CommandResult:
+    cmd: list[str]
+    rc: int
+    """Return code"""
+    stderr: bytes
+    """Outputted stderr"""
+    stdout: bytes
+    """Outputted stdout"""
+
+    def ok(self):
+        if self.rc != 0:
+            raise subprocess.CalledProcessError(returncode=self.rc,
+                                                cmd=self.cmd,
+                                                stderr=self.stderr,
+                                                output=self.stdout)
+        return self
+
+    def json(self) -> Any:
+        self.ok()
+        return json.loads(self.stdout)
+
+
+@dataclasses.dataclass
+class NixSettings:
+    """Settings for invoking Nix"""
+    experimental_features: set[str] | None = None
+
+    def feature(self, *names: str):
+        self.experimental_features = (self.experimental_features
+                                      or set()) | set(names)
+        return self
+
+    def to_config(self) -> str:
+        config = ''
+
+        def serialise(value):
+            if type(value) in {str, int}:
+                return str(value)
+            elif type(value) in {list, set}:
+                return ' '.join(str(e) for e in value)
+            else:
+                raise ValueError(
+                    f'Value is unsupported in nix config: {value!r}')
+
+        def field_may(name, value, serialiser=serialise):
+            nonlocal config
+            if value is not None:
+                config += f'{name} = {serialiser(value)}\n'
+
+        field_may('experimental-features', self.experimental_features)
+        return config
+
+
+@dataclasses.dataclass
+class Nix:
+    test_root: Path
+
+    def hermetic_env(self):
+        # mirroring vars-and-functions.sh
+        home = self.test_root / 'test-home'
+        home.mkdir(parents=True, exist_ok=True)
+        return {
+            'NIX_STORE_DIR': self.test_root / 'store',
+            'NIX_LOCALSTATE_DIR': self.test_root / 'var',
+            'NIX_LOG_DIR': self.test_root / 'var/log/nix',
+            'NIX_STATE_DIR': self.test_root / 'var/nix',
+            'NIX_CONF_DIR': self.test_root / 'etc',
+            'NIX_DAEMON_SOCKET_PATH': self.test_root / 'daemon-socket',
+            'NIX_USER_CONF_FILES': '',
+            'HOME': home,
+        }
+
+    def make_env(self):
+        # We conservatively assume that people might want to successfully get
+        # some env through to the subprocess, so we override whatever is in the
+        # global env.
+        d = os.environ.copy()
+        d.update(self.hermetic_env())
+        return d
+
+    def call(self, cmd: list[str], extra_env: dict[str, str] = {}):
+        """
+        Calls a process in the test environment.
+        """
+        env = self.make_env()
+        env.update(extra_env)
+        proc = subprocess.Popen(
+            cmd,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+            cwd=self.test_root,
+            env=env,
+        )
+        (stdout, stderr) = proc.communicate()
+        rc = proc.returncode
+        return CommandResult(cmd=cmd, rc=rc, stdout=stdout, stderr=stderr)
+
+    def nix(self,
+            cmd: list[str],
+            settings: NixSettings = NixSettings(),
+            extra_env: dict[str, str] = {}):
+        extra_env = extra_env.copy()
+        extra_env.update({'NIX_CONFIG': settings.to_config()})
+        return self.call(['nix', *cmd], extra_env)
+
+    def eval(
+        self, expr: str,
+        settings: NixSettings = NixSettings()) -> CommandResult:
+        # clone due to reference-shenanigans
+        settings = dataclasses.replace(settings).feature('nix-command')
+
+        return self.nix(['eval', '--json', '--expr', expr], settings=settings)