add buildbot extension for autoscaling nix builders

buildbot-ext/buildbot_autoscale_ext/tests/test_configurator.py

@@ -0,0 +1,59 @@
+from __future__ import annotations
+
+import logging
+from dataclasses import dataclass, field
+
+import pytest
+
+from buildbot_autoscale_ext.configurator import AutoscaleConfigurator
+from buildbot_autoscale_ext.settings import AutoscaleSettings
+from buildbot_autoscale_ext.steps import CapacityGateStep, CapacityReleaseStep
+
+
+@dataclass
+class FakeFactory:
+    steps: list[object] = field(default_factory=list)
+
+
+@dataclass
+class FakeBuilder:
+    name: str
+    factory: FakeFactory
+
+
+def test_patches_nix_builders() -> None:
+    cfg = {
+        "builders": [
+            FakeBuilder("proj/nix-build", FakeFactory(["original"])),
+            FakeBuilder("proj/eval", FakeFactory(["eval"])),
+        ]
+    }
+
+    AutoscaleConfigurator(AutoscaleSettings(daemon_socket="/tmp/daemon.sock")).configure(cfg)
+
+    patched_steps = cfg["builders"][0].factory.steps
+    assert isinstance(patched_steps[0], CapacityGateStep)
+    assert patched_steps[1] == "original"
+    assert isinstance(patched_steps[-1], CapacityReleaseStep)
+
+    untouched_steps = cfg["builders"][1].factory.steps
+    assert untouched_steps == ["eval"]
+
+
+def test_empty_builders_no_error() -> None:
+    cfg = {"builders": []}
+    AutoscaleConfigurator(AutoscaleSettings(daemon_socket="/tmp/daemon.sock")).configure(cfg)
+
+
+def test_startup_log_contains_patched_names(caplog: pytest.LogCaptureFixture) -> None:
+    caplog.set_level(logging.INFO)
+    cfg = {
+        "builders": [
+            FakeBuilder("one/nix-build", FakeFactory()),
+            FakeBuilder("two/eval", FakeFactory()),
+        ]
+    }
+
+    AutoscaleConfigurator(AutoscaleSettings(daemon_socket="/tmp/daemon.sock")).configure(cfg)
+
+    assert "one/nix-build" in caplog.text