Suppress offset text in ConciseDateFormatter when largest scale is in years

Add tests for offset text in ConciseDateFormatter

Author: harrymknight

lib/matplotlib/dates.py

@@ -802,6 +802,9 @@ def format_ticks(self, values):
         # 3: hours, 4: minutes, 5: seconds, 6: microseconds
         for level in range(5, -1, -1):
             if len(np.unique(tickdate[:, level])) > 1:
+                # level is less than 2 so a year is already present in the axis
+                if (level < 2):
+                    self.show_offset = False
                 break
             elif level == 0:
                 # all tickdate are the same, so only micros might be different

lib/matplotlib/tests/test_dates.py

@@ -523,6 +523,30 @@ def _create_auto_date_locator(date1, date2):
         assert strings == expected
 
 
+@pytest.mark.parametrize('t_delta, expected', [
+    (datetime.timedelta(seconds=0.01), '1997-Jan-01 00:00'),
+    (datetime.timedelta(minutes=1), '1997-Jan-01 00:01'),
+    (datetime.timedelta(hours=1), '1997-Jan-01'),
+    (datetime.timedelta(days=1), '1997-Jan-02'),
+    (datetime.timedelta(weeks=1), '1997-Jan'),
+    (datetime.timedelta(weeks=26), ''),
+    (datetime.timedelta(weeks=520), '')
+])
+def test_concise_formatter_show_offset(t_delta, expected):
+    d1 = datetime.datetime(1997, 1, 1)
+    d2 = d1 + t_delta
+
+    fig, ax = plt.subplots()
+    locator = mdates.AutoDateLocator()
+    formatter = mdates.ConciseDateFormatter(locator)
+    ax.xaxis.set_major_locator(locator)
+    ax.xaxis.set_major_formatter(formatter)
+
+    ax.plot([d1, d2], [0, 0])
+    fig.canvas.draw()
+    assert formatter.get_offset() == expected
+
+
 @pytest.mark.parametrize('t_delta, expected', [
     (datetime.timedelta(weeks=52 * 200),
      ['$\\mathdefault{%d}$' % (t, ) for t in range(1980, 2201, 20)]),