Add test for year locator

Author: theOehrly

lib/matplotlib/tests/test_dates.py

@@ -964,6 +964,41 @@ def test_yearlocator_pytz():
     assert st == expected
 
 
+def test_YearLocator():
+    def _create_year_locator(date1, date2, **kwargs):
+        locator = mdates.YearLocator(**kwargs)
+        locator.create_dummy_axis()
+        locator.set_view_interval(mdates.date2num(date1),
+                                  mdates.date2num(date2))
+        return locator
+
+    d1 = datetime.datetime(1990, 1, 1)
+    results = ([datetime.timedelta(weeks=52 * 200),
+                {'base': 20, 'month': 1, 'day': 1},
+                ['1980-01-01 00:00:00+00:00', '2000-01-01 00:00:00+00:00',
+                 '2020-01-01 00:00:00+00:00', '2040-01-01 00:00:00+00:00',
+                 '2060-01-01 00:00:00+00:00', '2080-01-01 00:00:00+00:00',
+                 '2100-01-01 00:00:00+00:00', '2120-01-01 00:00:00+00:00',
+                 '2140-01-01 00:00:00+00:00', '2160-01-01 00:00:00+00:00',
+                 '2180-01-01 00:00:00+00:00', '2200-01-01 00:00:00+00:00']
+                ],
+               [datetime.timedelta(weeks=52 * 200),
+                {'base': 20, 'month': 5, 'day': 16},
+                ['1980-05-16 00:00:00+00:00', '2000-05-16 00:00:00+00:00',
+                 '2020-05-16 00:00:00+00:00', '2040-05-16 00:00:00+00:00',
+                 '2060-05-16 00:00:00+00:00', '2080-05-16 00:00:00+00:00',
+                 '2100-05-16 00:00:00+00:00', '2120-05-16 00:00:00+00:00',
+                 '2140-05-16 00:00:00+00:00', '2160-05-16 00:00:00+00:00',
+                 '2180-05-16 00:00:00+00:00', '2200-05-16 00:00:00+00:00']
+                ],
+               )
+
+    for delta, arguments, expected in results:
+        d2 = d1 + delta
+        locator = _create_year_locator(d1, d2, **arguments)
+        assert list(map(str, mdates.num2date(locator()))) == expected
+
+
 def test_DayLocator():
     with pytest.raises(ValueError):
         mdates.DayLocator(interval=-1)