diff --git a/tests/test_capability_check.py b/tests/test_capability_check.py
new file mode 100644
index 0000000..3e13737
--- /dev/null
+++ b/tests/test_capability_check.py
@@ -0,0 +1,106 @@
+"""Tests for obliteratus.capability_check."""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+
+class TestCapabilityCheckImport:
+    def test_import(self):
+        from obliteratus.capability_check import capability_check  # noqa: F401
+
+    def test_quick_subjects_defined(self):
+        from obliteratus.capability_check import QUICK_SUBJECTS
+
+        assert len(QUICK_SUBJECTS) >= 3
+        assert all(s.startswith("mmlu_") for s in QUICK_SUBJECTS)
+
+
+class TestRunLmEval:
+    @patch("obliteratus.capability_check.subprocess.run")
+    def test_calls_lm_eval(self, mock_run, tmp_path):
+        from obliteratus.capability_check import _run_lm_eval
+
+        # Create fake results
+        results_dir = tmp_path / "results" / "fake_model"
+        results_dir.mkdir(parents=True)
+        results_file = results_dir / "results_2026.json"
+        results_file.write_text(json.dumps({
+            "results": {"mmlu": {"acc,none": 0.85}},
+        }))
+
+        mock_run.return_value = MagicMock(returncode=0, stdout="", stderr="")
+
+        result = _run_lm_eval("fake/model", "mmlu", 5, "cpu", str(tmp_path / "results"))
+        assert result["results"]["mmlu"]["acc,none"] == 0.85
+        mock_run.assert_called_once()
+
+    @patch("obliteratus.capability_check.subprocess.run")
+    def test_raises_on_failure(self, mock_run, tmp_path):
+        from obliteratus.capability_check import _run_lm_eval
+
+        mock_run.return_value = MagicMock(returncode=1, stdout="", stderr="error")
+
+        with pytest.raises(RuntimeError, match="lm-eval exited"):
+            _run_lm_eval("fake/model", "mmlu", 5, "cpu", str(tmp_path))
+
+
+class TestCapabilityCheck:
+    @patch("obliteratus.capability_check._run_lm_eval")
+    def test_computes_delta(self, mock_lm_eval, tmp_path):
+        from obliteratus.capability_check import capability_check
+
+        mock_lm_eval.side_effect = [
+            {"results": {"mmlu": {"acc,none": 0.81}}},  # abliterated
+            {"results": {"mmlu": {"acc,none": 0.87}}},  # stock
+        ]
+
+        result = capability_check(
+            "fake/abliterated", "fake/stock",
+            device="cpu", output_dir=str(tmp_path),
+        )
+
+        assert result["abliterated_acc"] == 0.81
+        assert result["stock_acc"] == 0.87
+        assert result["delta_pp"] == -6.0
+
+    @patch("obliteratus.capability_check._run_lm_eval")
+    def test_quick_mode(self, mock_lm_eval, tmp_path):
+        from obliteratus.capability_check import QUICK_SUBJECTS, capability_check
+
+        mock_lm_eval.side_effect = [
+            {"results": {s: {"acc,none": 0.8} for s in QUICK_SUBJECTS}},
+            {"results": {s: {"acc,none": 0.9} for s in QUICK_SUBJECTS}},
+        ]
+
+        result = capability_check(
+            "fake/abliterated", "fake/stock",
+            device="cpu", quick=True, output_dir=str(tmp_path),
+        )
+
+        assert result["tasks"] == ",".join(QUICK_SUBJECTS)
+        assert abs(result["abliterated_acc"] - 0.8) < 0.01
+
+    @patch("obliteratus.capability_check._run_lm_eval")
+    def test_saves_summary(self, mock_lm_eval, tmp_path):
+        from obliteratus.capability_check import capability_check
+
+        mock_lm_eval.side_effect = [
+            {"results": {"mmlu": {"acc,none": 0.85}}},
+            {"results": {"mmlu": {"acc,none": 0.87}}},
+        ]
+
+        capability_check(
+            "fake/abliterated", "fake/stock",
+            device="cpu", output_dir=str(tmp_path),
+        )
+
+        summary_path = tmp_path / "capability_summary.json"
+        assert summary_path.exists()
+        summary = json.loads(summary_path.read_text())
+        assert "delta_pp" in summary
+        assert summary["method"] == "lm-eval-harness 0-shot log-likelihood"