feat(metrics): add rate + blockstats/netstat/fsinfo parsing helpers

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/tests/test_metrics_history.py

@@ -0,0 +1,40 @@
+from app.services import metrics_history as mh
+
+
+def test_compute_rate_normal():
+    assert mh.compute_rate(100, 160, 2.0) == 30.0
+
+def test_compute_rate_no_prev():
+    assert mh.compute_rate(None, 160, 2.0) is None
+
+def test_compute_rate_counter_reset():
+    assert mh.compute_rate(500, 10, 2.0) == 0.0
+
+def test_compute_rate_zero_dt():
+    assert mh.compute_rate(100, 200, 0) is None
+
+def test_parse_blockstats_sums_devices():
+    text = (
+        "drive-scsi0: rd_bytes=10 wr_bytes=20 rd_operations=100 wr_operations=50 flush_operations=1\n"
+        "drive-scsi1: rd_bytes=5 wr_bytes=5 rd_operations=7 wr_operations=3 flush_operations=0\n"
+    )
+    assert mh.parse_blockstats(text) == (107, 53)
+
+def test_parse_blockstats_empty():
+    assert mh.parse_blockstats("") == (0, 0)
+
+def test_parse_netstat_filters_by_vmid():
+    rows = [
+        {"dev": "tap114i0", "vmid": "114", "in": "1000", "out": "2000"},
+        {"dev": "tap114i1", "vmid": "114", "in": "10", "out": "20"},
+        {"dev": "tap200i0", "vmid": "200", "in": "9", "out": "9"},
+    ]
+    out = mh.parse_netstat(rows, 114)
+    assert out == {"tap114i0": (1000, 2000), "tap114i1": (10, 20)}
+
+def test_aggregate_fsinfo_sums():
+    disks = [{"used": 10, "total": 40}, {"used": 5, "total": 20}]
+    assert mh.aggregate_fsinfo(disks) == (15, 60)
+
+def test_aggregate_fsinfo_empty():
+    assert mh.aggregate_fsinfo([]) == (0, 0)