Only zero is empty, and the last day is worth reading

tests/test_plugins/test_supply_history.py

@@ -8,6 +8,8 @@ purchasing decision.
 
 from datetime import datetime, timedelta, timezone
 
+import pytest
+
 from plugins.printers.services.supply_history import (
     analyse, band, burn_rate, current_run, find_replacements, normalise,
     orderlist, soonest,
@@ -113,28 +115,69 @@ def test_live_level_drives_the_countdown_not_the_stored_one():
     assert result['daysleft'] == 1              # 20 / 20, not 40 / 20
 
 
-def test_a_nearly_empty_cartridge_reads_as_empty_not_as_weeks_away():
-    """1% draining a tenth of a point a day computes to ten days. It is out."""
-    result = analyse(series([2.0, 1.7, 1.4, 1.1]), currentlevel=1)
+def test_a_nearly_empty_cartridge_keeps_its_real_countdown():
+    """Only zero is empty.
+
+    This used to floor everything at or below 5% to daysleft 0, so 1% draining
+    a tenth of a point a day was reported as gone. It has ten days in it, and
+    ten days is the only thing the row exists to say. Flooring it put the
+    cartridge beside ones that genuinely are empty with no way back to the
+    difference.
+    """
+    # 3.0 down to 1.0 at a tenth of a point a day: a real, slow, measured drop.
+    slow = [round(3.0 - 0.1 * i, 2) for i in range(21)]
+    result = analyse(series(slow), currentlevel=1)
+
+    assert result['daysleft'] == pytest.approx(10, abs=0.1)
+
+
+def test_a_cartridge_with_hours_left_is_not_reported_as_empty():
+    """The other half of the floor: int() truncated the division, so anything
+    under a full day became 0 and read as empty. A cartridge with six hours in
+    it still prints."""
+    result = analyse(series([100, 75, 50, 25]), currentlevel=6)
+
+    assert 0 < result['daysleft'] < 1
+    assert round(result['daysleft'] * 24) == 6
+
+
+def test_an_actual_zero_is_still_empty():
+    """The half that must not regress. Zero means spent, and spent is ordered
+    first."""
+    result = analyse(series([2.0, 1.7, 1.4, 1.1]), currentlevel=0)
 
     assert result['daysleft'] == 0
 
 
 def test_empty_sorts_ahead_of_a_fast_healthy_cartridge():
-    empty = analyse(series([2.0, 1.7, 1.4, 1.1]), currentlevel=1)
+    empty = analyse(series([2.0, 1.7, 1.4, 1.1]), currentlevel=0)
     healthy = analyse(series([100, 80, 60, 40]))
 
     assert empty['daysleft'] < healthy['daysleft']
 
 
-def test_a_low_live_level_is_actionable_without_any_history():
+def test_an_empty_live_level_is_actionable_without_any_history():
     """A printer new to Zabbix still reports it is out of toner."""
-    result = analyse([], currentlevel=1)
+    result = analyse([], currentlevel=0)
 
     assert result['daysleft'] == 0
     assert result['reason'] is None
 
 
+def test_a_low_live_level_with_no_history_cannot_be_counted_down():
+    """A rate needs two readings. At 1% with none, there is nothing to divide.
+
+    Previously the 5% floor answered this by asserting daysleft 0, which was
+    right by accident and wrong in general - it said "empty" about a level
+    nobody had watched move. It reports no estimate and says why; the report
+    lists it under "No estimate yet" rather than on the order list.
+    """
+    result = analyse([], currentlevel=1)
+
+    assert result['daysleft'] is None
+    assert result['reason'] == 'no history'
+
+
 def test_no_history_and_a_healthy_level_still_says_no_history():
     result = analyse([], currentlevel=80)