Fix issue with UnitsRegistry being overriden

before

@@ -0,0 +1,76 @@
+glue/viewers/histogram/qt/tests/test_data_viewer.py HERE3 <matplotlib.dates.AutoDateLocator object at 0x7f6e4aac9340> <matplotlib.dates.AutoDateFormatter object at 0x7f6e4aac9580>
+HERE1 1970-04-11
+HERE2 719263.0
+HERE1 1971-02-05
+HERE2 719563.0
+HERE1 1970-04-11
+HERE2 719263.0
+HERE1 1971-02-05
+HERE2 719563.0
+HERE1 1970-04-14
+HERE2 719266.0
+HERE1 1971-02-05
+HERE2 719563.0
+HERE3 <matplotlib.dates.AutoDateLocator object at 0x7f6e03595730> <matplotlib.dates.AutoDateFormatter object at 0x7f6e03595940>
+HERE3 <matplotlib.dates.AutoDateLocator object at 0x7f6e035e2cd0> <matplotlib.dates.AutoDateFormatter object at 0x7f6e03595bb0>
+HERE1 1970-04-14
+HERE2 719266.0
+HERE1 1971-02-05
+HERE2 719563.0
+.
+glue/viewers/scatter/qt/tests/test_data_viewer.py HERE3 <matplotlib.dates.AutoDateLocator object at 0x7f6e024d1910> <matplotlib.dates.AutoDateFormatter object at 0x7f6e024d1b20>
+HERE1 1970-03-30
+HERE2 719251.0
+HERE1 1971-02-17
+HERE2 719575.0
+HERE1 1970-03-30
+HERE2 719251.0
+HERE1 1971-02-17
+HERE2 719575.0
+HERE1 []
+HERE1 []
+HERE1 1970-03-30
+HERE2 719251.0
+HERE1 1971-02-17
+HERE2 719575.0
+HERE3 <matplotlib.dates.AutoDateLocator object at 0x7f6e024f1dc0> <matplotlib.dates.AutoDateFormatter object at 0x7f6e024f1fd0>
+HERE1 1970-07-08
+HERE2 719351.0
+HERE1 1971-05-28
+HERE2 719675.0
+HERE1 1970-03-30
+HERE2 719251.0
+HERE1 1971-02-17
+HERE2 719575.0
+HERE1 1970-07-08
+HERE2 719351.0
+HERE1 1971-05-28
+HERE2 719675.0
+HERE1 []
+HERE1 []
+HERE1 []
+HERE1 []
+HERE1 1970-03-30
+HERE2 719251.0
+HERE1 1971-02-17
+HERE2 719575.0
+HERE1 1970-03-30
+HERE2 719251.0
+HERE1 1971-02-17
+HERE2 719575.0
+HERE1 1970-04-14
+HERE2 719266.0
+HERE1 1971-02-17
+HERE2 719575.0
+HERE3 <matplotlib.dates.AutoDateLocator object at 0x7f6e02483340> <matplotlib.dates.AutoDateFormatter object at 0x7f6e02483550>
+HERE3 <matplotlib.dates.AutoDateLocator object at 0x7f6e0250c8e0> <matplotlib.dates.AutoDateFormatter object at 0x7f6e024837c0>
+HERE1 1970-04-14
+HERE2 719266.0
+HERE1 1971-02-17
+HERE2 719575.0
+HERE1 []
+HERE1 []
+HERE1 []
+HERE1 []
+HERE1 []
+HERE1 []

glue/_mpl_backend.py

@@ -1,4 +1,5 @@
 import os
+import numpy as np
 
 
 class MatplotlibBackendSetter(object):
@@ -46,3 +47,9 @@ def set_mpl_backend():
     # Explicitly switch backend
     from matplotlib.pyplot import switch_backend
     switch_backend('agg')
+
+    # We override the datetime64 units.registry entry to use our class. We do
+    # this here to make sure that rcdefaults hasn't reset this.
+    import matplotlib.units as units
+    from glue.utils.matplotlib import Datetime64Converter
+    units.registry[np.datetime64] = Datetime64Converter()

glue/conftest.py

@@ -45,6 +45,9 @@ def pytest_configure(config):
 
     os.environ['GLUE_TESTING'] = 'True'
 
+    from glue._mpl_backend import set_mpl_backend
+    set_mpl_backend()
+
     if config.getoption('no_optional_skip'):
         from glue.tests import helpers
         for attr in helpers.__dict__: