tests/functional2/nix: fix config serialization

Currently, the typecheck for the config values is only done
half-heartedly only checking if something is either a list or non-list
item, but not checking what type the list items are

this commit fixes the typecheck and adds test for proper serialization

Change-Id: Ifd93842b19b1dd870bdb3af0c000243b4380e7aa

tests/functional2/testlib/fixtures/nix.py

@@ -8,6 +8,7 @@ from collections.abc import Callable, Generator
 import pytest
 
 from functional2.testlib.commands import CommandResult, Command
+from functional2.testlib.utils import is_value_of_type
 
 
 @dataclasses.dataclass
@@ -43,11 +44,13 @@ class NixSettings:
         config = ""
 
         def serialise(value: Any) -> str:
-            if type(value) in {str, int}:
+            # TODO(Commentator2.0): why exactly are ints supported?
+            if is_value_of_type(value, set[str | int]):
+                return " ".join(serialise(e) for e in value)
+            if is_value_of_type(value, str | int):
                 return str(value)
-            if type(value) in {list, set}:
-                return " ".join(str(e) for e in value)
-            msg = f"Value is unsupported in nix config: {value!r}"
+
+            msg = f"Value is unsupported in nix config: {value!r}, must bei either `str|int` or `set[str|int]`"
             raise ValueError(msg)
 
         def field_may(name: str, value: Any, serializer: Callable[[Any], str] = serialise):

tests/functional2/testlib/fixtures/test_nix.py

@@ -0,0 +1,72 @@
+from pathlib import Path
+
+import pytest
+
+from functional2.testlib.fixtures.nix import NixSettings
+
+
+def test_nix_settings_serializes_xf():
+    settings = NixSettings(nix_store_dir=Path("/store/nix"))
+    settings.feature("a", "b")
+
+    expected = "experimental-features = a b\n"
+    assert settings.to_config() == expected
+
+
+def test_nix_settings_serializes_store():
+    settings = NixSettings(nix_store_dir=Path("/store/nix"))
+    settings.store = "some/path"
+
+    expected = "store = some/path\n"
+    assert settings.to_config() == expected
+
+
+def test_nix_settings_serializes_both():
+    settings = NixSettings(nix_store_dir=Path("/store/nix"))
+    settings.feature("a", "b")
+    settings.store = "some/path"
+
+    expected = "experimental-features = a b\nstore = some/path\n"
+    assert settings.to_config() == expected
+
+
+def test_nix_settings_ser_fails_bad_top_level_type():
+    settings = NixSettings(nix_store_dir=Path("/store/nix"))
+    settings.experimental_features = {"a": "b"}  # type: ignore we are testing the types here
+
+    with pytest.raises(ValueError, match="Value is unsupported in nix config: {'a': 'b'}"):
+        settings.to_config()
+
+
+def test_nix_settings_ser_fails_bad_sub_type():
+    settings = NixSettings(nix_store_dir=Path("/store/nix"))
+    settings.experimental_features = [["a", "b"], "c"]  # type: ignore we are testing the types here
+
+    with pytest.raises(ValueError, match="Value is unsupported in nix config: .+"):
+        settings.to_config()
+
+
+def test_nix_settings_fails_without_store_and_store_dir():
+    settings = NixSettings()
+
+    with pytest.raises(
+        AssertionError,
+        match="Failing to set either nix_store_dir or store will cause accidental use of the system store.",
+    ):
+        settings.to_config()
+
+
+def test_nix_settings_to_env_overlay_no_store_dir():
+    settings = NixSettings()
+    settings.store = "some/path"
+
+    expected = {"NIX_CONFIG": "store = some/path\n"}
+    assert settings.to_env_overlay() == expected
+
+
+def test_nix_settings_to_env_overlay_store_dir():
+    settings = NixSettings()
+    settings.nix_store_dir = Path("/some/path")
+
+    expected = {"NIX_CONFIG": "", "NIX_STORE_DIR": "/some/path"}
+    assert settings.to_env_overlay() == expected