diff --git a/tests/test_bench_run.py b/tests/test_bench_run.py
new file mode 100644
index 0000000..6bfcdc5
--- /dev/null
+++ b/tests/test_bench_run.py
@@ -0,0 +1,41 @@
+import unittest
+
+from atex.bench.run import BenchResult, format_results_md
+
+
+class TestFormatResultsMarkdown(unittest.TestCase):
+    def test_empty_results_contains_only_markdown_header(self):
+        self.assertEqual(
+            format_results_md([]),
+            "| backend | ingest_n | ingest_ms | throughput (entries/s) | recall@1 | recall@3 | recall@5 | avg query (ms) | p99 (ms) | cold-start (ms) |\n"
+            "|---|---:|---:|---:|---:|---:|---:|---:|---:|---:|",
+        )
+
+    def test_formats_zero_and_fractional_metrics_with_documented_precision(self):
+        result = BenchResult(
+            name="boundary",
+            ingest_n=0,
+            ingest_wall_s=0.00004,
+            ingest_throughput_entries_per_s=0.5,
+            recall_at_1=0.005,
+            recall_at_3=0.995,
+            recall_at_5=1.0,
+            avg_query_ms=0.0,
+            p99_query_ms=1.25,
+            cold_start_ms=0.0,
+        )
+
+        self.assertEqual(
+            format_results_md([result]),
+            "| backend | ingest_n | ingest_ms | throughput (entries/s) | recall@1 | recall@3 | recall@5 | avg query (ms) | p99 (ms) | cold-start (ms) |\n"
+            "|---|---:|---:|---:|---:|---:|---:|---:|---:|---:|\n"
+            "| boundary | 0 | 0.0 | 0 | 0% | 100% | 100% | 0.0 | 1.25 | 0.0 |",
+        )
+
+    def test_rejects_non_result_rows(self):
+        with self.assertRaises(AttributeError):
+            format_results_md([object()])
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)