Order the supplies card by how empty the cartridge is

Rows sorted on iscritical then on printer NAME. Critical is everything
at or below 5%, so a cartridge at 5% and one at 0% tied on the first key
and the alphabet decided which came first.

Wrong order on its own, and worse than it looks: the dashboard queue
keeps only the first few rows per source, so a printer that was
genuinely empty was truncated off the card while a fuller one held its
place. Reported from the floor as "starts at 5% and hides one at 0%",
which is exactly the two bugs compounding.

remaining is already normalised for waste cartridges - a full waste bin
reads as low remaining - so one ascending sort is worst-first for every
supply type, and iscritical falls out of it rather than needing its own
key. Name only breaks ties.

worstremaining is carried on the row because the supplies list is
rendered to text ("Black 0%") before it reaches the client, so the
number the sort needs is gone by then.

The toner forecast report was already worst-first (it sorts on daysleft)
and is unchanged.

Scope: product
(cherry picked from commit 6644a07ae1)

tests/test_plugins/test_supplies_card_ordering.py

@@ -0,0 +1,101 @@
+"""The supplies card must put the emptiest cartridge first.
+
+It sorted on iscritical, then on PRINTER NAME. Critical is everything at or
+below 5%, so a cartridge at 5% and one at 0% tied on the first key and the
+alphabet decided the order.
+
+That is bad ordering on its own, and worse than it looks: the dashboard queue
+takes only the first few rows per source, so a printer that is genuinely empty
+was truncated out of the card while a fuller one held its place. The card
+existed to answer "what do I walk out and change today" and was answering it
+with the alphabet.
+"""
+from unittest.mock import patch
+
+import pytest
+
+
+def _call(client, auth_headers):
+    response = client.get('/api/printers/dashboard/supplies',
+                          headers=auth_headers)
+    assert response.status_code == 200
+    return response.get_json()['data']
+
+
+@pytest.fixture(autouse=True)
+def _clear_cache(app):
+    from shopdb.extensions import cache
+    cache.delete('printers_low_supplies')
+    yield
+    cache.delete('printers_low_supplies')
+
+
+def _printer(printerid, name, remaining, status='critical'):
+    return {
+        'printerid': printerid,
+        'printername': name,
+        'assetnumber': 'A{}'.format(printerid),
+        'location': 'Shop floor',
+        'mapx': None, 'mapy': None, 'levelid': None,
+        'supplies': [{
+            'name': 'Black Toner', 'level': remaining, 'remaining': remaining,
+            'status': status, 'iswaste': False, 'isdrum': False,
+            'partnumbers': [], 'lastseen': None, 'color': 'black',
+            'supplytype': 'toner',
+        }],
+    }
+
+
+def _patched(rows):
+    return patch('plugins.printers.api.asset_routes._get_low_supplies_data',
+                 return_value={'printers': rows,
+                               'summary': {'total_checked': len(rows),
+                                           'low': 0, 'critical': len(rows)}})
+
+
+def test_the_empty_cartridge_comes_before_the_nearly_empty_one(client,
+                                                               auth_headers):
+    """'Alpha' at 5% used to precede 'Zulu' at 0% purely on the name."""
+    with _patched([_printer(1, 'Alpha', 5), _printer(2, 'Zulu', 0)]):
+        data = _call(client, auth_headers)
+
+    order = [row['printername'] for row in data['rows']]
+    assert order == ['Zulu', 'Alpha']
+
+
+def test_rows_are_ordered_by_how_empty_they_are(client, auth_headers):
+    with _patched([_printer(1, 'Alpha', 4),
+                   _printer(2, 'Bravo', 0),
+                   _printer(3, 'Charlie', 2),
+                   _printer(4, 'Delta', 5)]):
+        data = _call(client, auth_headers)
+
+    remaining = [row['worstremaining'] for row in data['rows']]
+    assert remaining == sorted(remaining)
+    assert remaining == [0, 2, 4, 5]
+
+
+def test_a_zero_percent_printer_survives_the_queue_truncation(client,
+                                                              auth_headers):
+    """The dashboard queue keeps only the first few rows per source.
+
+    With five fuller printers whose names sort earlier, the empty one used to
+    fall off the end of the card entirely.
+    """
+    rows = [_printer(index, name, 5) for index, name in enumerate(
+        ['Alpha', 'Bravo', 'Charlie', 'Delta', 'Echo'], start=1)]
+    rows.append(_printer(6, 'Zulu', 0))
+
+    with _patched(rows):
+        data = _call(client, auth_headers)
+
+    # QUEUEPERSOURCE is 5 on the frontend; first place is what matters here.
+    assert data['rows'][0]['printername'] == 'Zulu'
+    assert [r['printername'] for r in data['rows'][:5]].count('Zulu') == 1
+
+
+def test_the_name_still_breaks_a_tie(client, auth_headers):
+    with _patched([_printer(1, 'Bravo', 3), _printer(2, 'Alpha', 3)]):
+        data = _call(client, auth_headers)
+
+    assert [row['printername'] for row in data['rows']] == ['Alpha', 'Bravo']