@@ -66,7 +66,7 @@ install:
   - activate test-environment
   - echo %PYTHON_VERSION% %TARGET_ARCH%
   # pytest-cov>=2.3.1 due to https://github.com/pytest-dev/pytest-cov/issues/124
-  - pip install -q "pytest!=3.3.0" "pytest-cov>=2.3.1" pytest-rerunfailures pytest-timeout pytest-xdist
+  - pip install -q "pytest!=3.3.0,>=3.2.0" "pytest-cov>=2.3.1" pytest-rerunfailures pytest-timeout pytest-xdist
 
   # Apply patch to `subprocess` on Python versions > 2 and < 3.6.3
   # https://github.com/matplotlib/matplotlib/issues/9176
 
@@ -52,7 +52,7 @@ env:
     - NUMPY=numpy
     - PANDAS=
     - PYPARSING=pyparsing
-    - PYTEST=pytest!=3.3.0
+    - PYTEST='pytest!=3.3.0,>=3.2.0'
     - PYTEST_COV=pytest-cov
     - PYTEST_PEP8=
     - SPHINX=sphinx
 
@@ -6442,7 +6442,7 @@ def hist(self, x, bins=None, range=None, density=None, weights=None,
         if normed is not None:
             warnings.warn("The 'normed' kwarg is deprecated, and has been "
                           "replaced by the 'density' kwarg.")
-            
+
         # basic input validation
         input_empty = np.size(x) == 0
         # Massage 'x' for processing.
 
@@ -720,9 +720,6 @@ def __init__(self, axes, pickradius=15):
         self.labelpad = rcParams['axes.labelpad']
         self.offsetText = self._get_offset_text()
 
-        self.majorTicks = []
-        self.minorTicks = []
-
         self.pickradius = pickradius
 
         # Initialize here for testing; later add API
@@ -780,12 +777,12 @@ def limit_range_for_scale(self, vmin, vmax):
         return self._scale.limit_range_for_scale(vmin, vmax, self.get_minpos())
 
     @property
-    @cbook.deprecated("2.1.1")
+    @cbook.deprecated("2.2.0")
     def unit_data(self):
         return self._units
 
     @unit_data.setter
-    @cbook.deprecated("2.1.1")
+    @cbook.deprecated("2.2.0")
     def unit_data(self, unit_data):
         self.set_units = unit_data
 
 
@@ -5,11 +5,12 @@
 from __future__ import (absolute_import, division, print_function,
                         unicode_literals)
 
-from collections import Iterable, OrderedDict
+from collections import OrderedDict
 import itertools
 
 import six
 
+
 import numpy as np
 
 import matplotlib.units as units
@@ -43,10 +44,12 @@ def convert(value, unit, axis):
 
         Parameters
         ----------
-        value: string, iterable
-            value or list of values to plot
-        unit:
-        axis:
+        value: string or iterable
+            value or list of values to be converted
+        unit: None
+            units to use for an axis with string data
+        axis: :class:`~matplotlib.axes.Axes`
+            axis on which the converted value is plotted
         """
         # dtype = object preserves numerical pass throughs
         values = np.atleast_1d(np.array(value, dtype=object))
@@ -76,7 +79,7 @@ def axisinfo(unit, axis):
         return units.AxisInfo(majloc=majloc, majfmt=majfmt)
 
     @staticmethod
-    def default_units(data=None, axis=None):
+    def default_units(data, axis):
         # the conversion call stack is supposed to be
         # default_units->axis_info->convert
         if axis.units is None:
@@ -130,11 +133,10 @@ def __init__(self, data=None):
         data: iterable
               sequence of string values
         """
-        if data is None:
-            data = ()
         self._mapping = OrderedDict()
         self._counter = itertools.count(start=0)
-        self.update(data)
+        if data is not None:
+            self.update(data)
 
     def update(self, data):
         """Maps new values to integer identifiers.
@@ -149,13 +151,9 @@ def update(self, data):
         TypeError
               If the value in data is not a string, unicode, bytes type
         """
+        data = np.atleast_1d(np.array(data, dtype=object))
 
-        if (isinstance(data, VALID_TYPES) or
-                not isinstance(data, Iterable)):
-            data = [data]
-
-        unsorted_unique = OrderedDict.fromkeys(data)
-        for val in unsorted_unique:
+        for val in OrderedDict.fromkeys(data):
             if not isinstance(val, VALID_TYPES):
                 raise TypeError("{val!r} is not a string".format(val=val))
             if val not in self._mapping:
 
@@ -121,13 +121,15 @@ def test_axisinfo(self):
     def test_default_units(self):
         assert isinstance(self.cc.default_units(["a"], self.ax), cat.UnitData)
 
+
 @pytest.fixture
 def ax():
     return plt.figure().subplots()
 
 PLOT_LIST = [Axes.scatter, Axes.plot, Axes.bar]
 PLOT_IDS = ["scatter", "plot", "bar"]
 
+
 class TestStrCategoryLocator(object):
     def test_StrCategoryLocator(self):
         locs = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
@@ -152,14 +154,14 @@ def test_StrCategoryFormatter(self, ax, ydata):
         unit = cat.UnitData(ydata)
         labels = cat.StrCategoryFormatter(unit)
         for i, d in enumerate(ydata):
-            assert labels(i, i) == d
+            assert labels(i, i) == cat.to_str(d)
 
     @pytest.mark.parametrize("ydata", cases, ids=ids)
     @pytest.mark.parametrize("plotter", PLOT_LIST, ids=PLOT_IDS)
     def test_StrCategoryFormatterPlot(self, ax, ydata, plotter):
         plotter(ax, range(len(ydata)), ydata)
         for i, d in enumerate(ydata):
-            assert ax.yaxis.major.formatter(i, i) == d
+            assert ax.yaxis.major.formatter(i, i) == cat.to_str(d)
         assert ax.yaxis.major.formatter(i+1, i+1) == ""
         assert ax.yaxis.major.formatter(0, None) == ""
 
@@ -254,17 +256,18 @@ def test_update_plot(self, ax, plotter):
     PLOT_BROKEN_LIST = [Axes.scatter,
                         pytest.param(Axes.plot, marks=pytest.mark.xfail),
                         pytest.param(Axes.bar, marks=pytest.mark.xfail)]
+
     PLOT_BROKEN_IDS = ["scatter", "plot", "bar"]
 
     @pytest.mark.parametrize("plotter", PLOT_BROKEN_LIST, ids=PLOT_BROKEN_IDS)
     @pytest.mark.parametrize("xdata", fvalues, ids=fids)
-    def test_plot_failures(self, ax, plotter, xdata):
+    def test_mixed_type_exception(self, ax, plotter, xdata):
         with pytest.raises(TypeError):
             plotter(ax, xdata, [1, 2])
 
     @pytest.mark.parametrize("plotter", PLOT_BROKEN_LIST, ids=PLOT_BROKEN_IDS)
     @pytest.mark.parametrize("xdata", fvalues, ids=fids)
-    def test_plot_failures_update(self, ax, plotter, xdata):
+    def test_mixed_type_update_exception(self, ax, plotter, xdata):
         with pytest.raises(TypeError):
             plotter(ax, [0, 3], [1, 3])
             plotter(ax, xdata, [1, 2])