diff --git a/conftest.py b/conftest.py
index acbdb0f0765..ac9d2731df7 100644
--- a/conftest.py
+++ b/conftest.py
@@ -5,5 +5,3 @@ def pytest_addoption(parser):
     """Add command-line flags for pytest."""
     parser.addoption("--run-flaky", action="store_true",
                      help="runs flaky tests")
-    parser.addoption("--skip-slow", action="store_true",
-                     help="skips slow tests")
diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index 3d82ed9b466..fa0d1f0d4ba 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -33,6 +33,11 @@ Bug fixes
   (:issue:`1359`).
   `Stephan Hoyer <https://github.com/shoyer>`_.
 
+- Ensure test suite works when runs from an installed version of xarray
+  (:issue:`1336`). Use ``@pytest.mark.slow`` instead of a custom flag to mark
+  slow tests.
+  By `Stephan Hoyer <https://github.com/shoyer>`_
+
 .. _whats-new.0.9.2:
 
 v0.9.2 (2 April, 2017)
diff --git a/xarray/tests/__init__.py b/xarray/tests/__init__.py
index a88c53ca75f..95af04b9e40 100644
--- a/xarray/tests/__init__.py
+++ b/xarray/tests/__init__.py
@@ -78,49 +78,36 @@
 
 # slighly simpler construction that the full functions.
 # Generally `pytest.importorskip('package')` inline is even easier
-requires_matplotlib = pytest.mark.skipif(not has_matplotlib, reason='requires matplotlib')
+requires_matplotlib = pytest.mark.skipif(
+    not has_matplotlib, reason='requires matplotlib')
+requires_scipy = pytest.mark.skipif(
+    not has_scipy, reason='requires scipy')
+requires_pydap = pytest.mark.skipif(
+    not has_pydap, reason='requires pydap')
+requires_netCDF4 = pytest.mark.skipif(
+    not has_netCDF4, reason='requires netCDF4')
+requires_h5netcdf = pytest.mark.skipif(
+    not has_h5netcdf, reason='requires h5netcdf')
+requires_pynio = pytest.mark.skipif(
+    not has_pynio, reason='requires pynio')
+requires_scipy_or_netCDF4 = pytest.mark.skipif(
+    not has_scipy and not has_netCDF4, reason='requires scipy or netCDF4')
+requires_dask = pytest.mark.skipif(
+    not has_dask, reason='requires dask')
+requires_bottleneck = pytest.mark.skipif(
+    not has_bottleneck, reason='requires bottleneck')
 
 
-def requires_scipy(test):
-    return test if has_scipy else pytest.mark.skip('requires scipy')(test)
-
-
-def requires_pydap(test):
-    return test if has_pydap else pytest.mark.skip('requires pydap.client')(test)
-
-
-def requires_netCDF4(test):
-    return test if has_netCDF4 else pytest.mark.skip('requires netCDF4')(test)
-
-
-def requires_h5netcdf(test):
-    return test if has_h5netcdf else pytest.mark.skip('requires h5netcdf')(test)
-
-
-def requires_pynio(test):
-    return test if has_pynio else pytest.mark.skip('requires pynio')(test)
-
-
-def requires_scipy_or_netCDF4(test):
-    return (test if has_scipy or has_netCDF4
-            else pytest.mark.skip('requires scipy or netCDF4')(test))
-
-
-def requires_dask(test):
-    return test if has_dask else pytest.mark.skip('requires dask')(test)
-
-
-def requires_bottleneck(test):
-    return test if has_bottleneck else pytest.mark.skip('requires bottleneck')(test)
-
+try:
+    _SKIP_FLAKY = not pytest.config.getoption("--run-flaky")
+except ValueError:
+    # Can't get config from pytest, e.g., because xarray is installed instead
+    # of being run from a development version (and hence conftests.py is not
+    # available). Don't run flaky tests.
+    _SKIP_FLAKY = True
 
 flaky = pytest.mark.skipif(
-    not pytest.config.getoption("--run-flaky"),
-    reason="set --run-flaky option to run flaky tests")
-
-slow = pytest.mark.skipif(
-    pytest.config.getoption("--skip-slow"),
-    reason="set --skip-slow option to run slow tests")
+    _SKIP_FLAKY, reason="set --run-flaky option to run flaky tests")
 
 
 class TestCase(unittest.TestCase):
diff --git a/xarray/tests/test_backends.py b/xarray/tests/test_backends.py
index e7a2dbd4381..d417fde4dda 100644
--- a/xarray/tests/test_backends.py
+++ b/xarray/tests/test_backends.py
@@ -27,7 +27,7 @@
 from . import (TestCase, requires_scipy, requires_netCDF4, requires_pydap,
                requires_scipy_or_netCDF4, requires_dask, requires_h5netcdf,
                requires_pynio, has_netCDF4, has_scipy, assert_allclose,
-               flaky, slow)
+               flaky)
 from .test_dataset import create_test_data
 
 try:
@@ -1118,21 +1118,21 @@ def test_4_autoclose_h5netcdf(self):
     @requires_dask
     @requires_netCDF4
     @flaky
-    @slow
+    @pytest.mark.slow
     def test_1_open_large_num_files_netcdf4(self):
         self.validate_open_mfdataset_large_num_files(engine=['netcdf4'])
 
     @requires_dask
     @requires_scipy
     @flaky
-    @slow
+    @pytest.mark.slow
     def test_2_open_large_num_files_scipy(self):
         self.validate_open_mfdataset_large_num_files(engine=['scipy'])
 
     @requires_dask
     @requires_pynio
     @flaky
-    @slow
+    @pytest.mark.slow
     def test_3_open_large_num_files_pynio(self):
         self.validate_open_mfdataset_large_num_files(engine=['pynio'])
 
@@ -1142,7 +1142,7 @@ def test_3_open_large_num_files_pynio(self):
     @requires_h5netcdf
     @flaky
     @pytest.mark.xfail
-    @slow
+    @pytest.mark.slow
     def test_4_open_large_num_files_h5netcdf(self):
         self.validate_open_mfdataset_large_num_files(engine=['h5netcdf'])
 
diff --git a/xarray/tests/test_dataset.py b/xarray/tests/test_dataset.py
index f9a3568b1ca..ec1e041deb1 100644
--- a/xarray/tests/test_dataset.py
+++ b/xarray/tests/test_dataset.py
@@ -3342,21 +3342,21 @@ def test_dir_unicode(data_set):
 @pytest.fixture(params=[1])
 def ds(request):
     if request.param == 1:
-        return Dataset({'z1': (['y', 'x'], np.random.randn(5, 20)),
-                        'z2': (['time', 'y'], np.random.randn(30, 5))},
-                       {'x': ('x', np.linspace(0, 1.0, 20)),
-                        'time': ('time', np.linspace(0, 1.0, 30)),
-                        'c': ('y', ['a', 'b', 'c', 'd', 'e']),
-                        'y': range(5)})
+        return Dataset({'z1': (['y', 'x'], np.random.randn(2, 8)),
+                        'z2': (['time', 'y'], np.random.randn(10, 2))},
+                       {'x': ('x', np.linspace(0, 1.0, 8)),
+                        'time': ('time', np.linspace(0, 1.0, 10)),
+                        'c': ('y', ['a', 'b']),
+                        'y': range(2)})
 
     if request.param == 2:
-        return Dataset({'z1': (['time', 'y'], np.random.randn(30, 5)),
-                        'z2': (['time'], np.random.randn(30)),
-                        'z3': (['x', 'time'], np.random.randn(20, 30))},
-                       {'x': ('x', np.linspace(0, 1.0, 20)),
-                        'time': ('time', np.linspace(0, 1.0, 30)),
-                        'c': ('y', ['a', 'b', 'c', 'd', 'e']),
-                        'y': range(5)})
+        return Dataset({'z1': (['time', 'y'], np.random.randn(10, 2)),
+                        'z2': (['time'], np.random.randn(10)),
+                        'z3': (['x', 'time'], np.random.randn(8, 10))},
+                       {'x': ('x', np.linspace(0, 1.0, 8)),
+                        'time': ('time', np.linspace(0, 1.0, 10)),
+                        'c': ('y', ['a', 'b']),
+                        'y': range(2)})
 
 
 def test_rolling_properties(ds):
@@ -3440,6 +3440,7 @@ def test_rolling_pandas_compat(center, window, min_periods):
                                ds_rolling['index'])
 
 
+@pytest.mark.slow
 @pytest.mark.parametrize('ds', (1, 2), indirect=True)
 @pytest.mark.parametrize('center', (True, False))
 @pytest.mark.parametrize('min_periods', (None, 1, 2, 3))
diff --git a/xarray/tests/test_plot.py b/xarray/tests/test_plot.py
index 621c1680492..cba03bd8361 100644
--- a/xarray/tests/test_plot.py
+++ b/xarray/tests/test_plot.py
@@ -17,6 +17,7 @@
 import numpy as np
 import pandas as pd
 from datetime import datetime
+import pytest
 
 from xarray import DataArray
 
@@ -26,9 +27,11 @@
                                _build_discrete_cmap,
                                _color_palette)
 
-from . import TestCase, requires_matplotlib, slow
+from . import TestCase, requires_matplotlib
 
 
+@pytest.mark.flaky
+@pytest.mark.skip(reason='maybe flaky')
 def text_in_fig():
     '''
     Return the set of all text in the figure
@@ -74,7 +77,7 @@ def pass_in_axis(self, plotmethod):
         plotmethod(ax=axes[0])
         self.assertTrue(axes[0].has_data())
 
-    @slow
+    @pytest.mark.slow
     def imshow_called(self, plotmethod):
         plotmethod()
         images = plt.gca().findobj(mpl.image.AxesImage)
@@ -101,7 +104,7 @@ def test_2d_before_squeeze(self):
     def test2d_uniform_calls_imshow(self):
         self.assertTrue(self.imshow_called(self.darray[:, :, 0].plot.imshow))
 
-    @slow
+    @pytest.mark.slow
     def test2d_nonuniform_calls_contourf(self):
         a = self.darray[:, :, 0]
         a.coords['dim_1'] = [2, 1, 89]
@@ -117,8 +120,9 @@ def test__infer_interval_breaks(self):
         self.assertArrayEqual([-0.5, 0.5, 1.5], _infer_interval_breaks([0, 1]))
         self.assertArrayEqual([-0.5, 0.5, 5.0, 9.5, 10.5],
                               _infer_interval_breaks([0, 1, 9, 10]))
-        self.assertArrayEqual(pd.date_range('20000101', periods=4) - np.timedelta64(12, 'h'),
-                              _infer_interval_breaks(pd.date_range('20000101', periods=3)))
+        self.assertArrayEqual(
+            pd.date_range('20000101', periods=4) - np.timedelta64(12, 'h'),
+            _infer_interval_breaks(pd.date_range('20000101', periods=3)))
 
         # make a bounded 2D array that we will center and re-infer
         xref, yref = np.meshgrid(np.arange(6), np.arange(5))
@@ -141,7 +145,7 @@ def test_datetime_dimension(self):
         ax = plt.gca()
         self.assertTrue(ax.has_data())
 
-    @slow
+    @pytest.mark.slow
     def test_convenient_facetgrid(self):
         a = easy_array((10, 15, 4))
         d = DataArray(a, dims=['y', 'x', 'z'])
@@ -158,7 +162,7 @@ def test_convenient_facetgrid(self):
         with self.assertRaisesRegexp(ValueError, '[Ff]acet'):
             d[0].plot(x='x', y='y', col='z', ax=plt.gca())
 
-    @slow
+    @pytest.mark.slow
     def test_subplot_kws(self):
         a = easy_array((10, 15, 4))
         d = DataArray(a, dims=['y', 'x', 'z'])
@@ -173,7 +177,7 @@ def test_subplot_kws(self):
             except AttributeError:
                 self.assertEqual(ax.get_axis_bgcolor(), 'r')
 
-    @slow
+    @pytest.mark.slow
     def test_plot_size(self):
         self.darray[:, 0, 0].plot(figsize=(13, 5))
         assert tuple(plt.gcf().get_size_inches()) == (13, 5)
@@ -199,7 +203,7 @@ def test_plot_size(self):
         with self.assertRaisesRegexp(ValueError, 'cannot provide `aspect`'):
             self.darray.plot(aspect=1)
 
-    @slow
+    @pytest.mark.slow
     def test_convenient_facetgrid_4d(self):
         a = easy_array((10, 15, 2, 3))
         d = DataArray(a, dims=['y', 'x', 'columns', 'rows'])
@@ -254,7 +258,7 @@ def test_primitive_returned(self):
         p = self.darray.plot.line()
         self.assertTrue(isinstance(p[0], mpl.lines.Line2D))
 
-    @slow
+    @pytest.mark.slow
     def test_plot_nans(self):
         self.darray[1] = np.nan
         self.darray.plot.line()
@@ -306,7 +310,7 @@ def test_primitive_returned(self):
         h = self.darray.plot.hist()
         self.assertTrue(isinstance(h[-1][0], mpl.patches.Rectangle))
 
-    @slow
+    @pytest.mark.slow
     def test_plot_nans(self):
         self.darray[0, 0, 0] = np.nan
         self.darray.plot.hist()
@@ -335,7 +339,7 @@ def test_center(self):
         self.assertIsNone(cmap_params['levels'])
         self.assertIsNone(cmap_params['norm'])
 
-    @slow
+    @pytest.mark.slow
     def test_integer_levels(self):
         data = self.data + 1
 
@@ -475,13 +479,13 @@ def setUp(self):
         self.data_min = distance.min()
         self.data_max = distance.max()
 
-    @slow
+    @pytest.mark.slow
     def test_recover_from_seaborn_jet_exception(self):
         pal = _color_palette('jet', 4)
         self.assertTrue(type(pal) == np.ndarray)
         self.assertEqual(len(pal), 4)
 
-    @slow
+    @pytest.mark.slow
     def test_build_discrete_cmap(self):
         for (cmap, levels, extend, filled) in [('jet', [0, 1], 'both', False),
                                                ('hot', [-4, 4], 'max', True)]:
@@ -497,7 +501,7 @@ def test_build_discrete_cmap(self):
             else:
                 self.assertEqual(ncmap.colorbar_extend, 'max')
 
-    @slow
+    @pytest.mark.slow
     def test_discrete_colormap_list_of_levels(self):
         for extend, levels in [('max', [-1, 2, 4, 8, 10]),
                                ('both', [2, 5, 10, 11]),
@@ -514,7 +518,7 @@ def test_discrete_colormap_list_of_levels(self):
                     self.assertEqual('max', primitive.cmap.colorbar_extend)
                 self.assertEqual(len(levels) - 1, len(primitive.cmap.colors))
 
-    @slow
+    @pytest.mark.slow
     def test_discrete_colormap_int_levels(self):
         for extend, levels, vmin, vmax in [('neither', 7, None, None),
                                            ('neither', 7, None, 20),
@@ -821,17 +825,17 @@ def test_facetgrid_cmap(self):
         d = DataArray(data, dims=['x', 'y', 'time'])
         fg = d.plot.pcolormesh(col='time')
         # check that all color limits are the same
-        self.assertTrue(len(set(m.get_clim() for m in fg._mappables)) == 1)
+        self.assertEqual(len(set(m.get_clim() for m in fg._mappables)), 1)
         # check that all colormaps are the same
-        self.assertTrue(len(set(m.get_cmap().name for m in fg._mappables)) == 1)
+        self.assertEqual(len(set(m.get_cmap().name for m in fg._mappables)), 1)
 
 
-@slow
+@pytest.mark.slow
 class TestContourf(Common2dMixin, PlotTestCase):
 
     plotfunc = staticmethod(xplt.contourf)
 
-    @slow
+    @pytest.mark.slow
     def test_contourf_called(self):
         # Having both statements ensures the test works properly
         self.assertFalse(self.contourf_called(self.darray.plot.imshow))
@@ -841,7 +845,7 @@ def test_primitive_artist_returned(self):
         artist = self.plotmethod()
         self.assertTrue(isinstance(artist, mpl.contour.QuadContourSet))
 
-    @slow
+    @pytest.mark.slow
     def test_extend(self):
         artist = self.plotmethod()
         self.assertEqual(artist.extend, 'neither')
@@ -859,7 +863,7 @@ def test_extend(self):
         artist = self.plotmethod(vmin=-10, vmax=0)
         self.assertEqual(artist.extend, 'max')
 
-    @slow
+    @pytest.mark.slow
     def test_2d_coord_names(self):
         self.plotmethod(x='x2d', y='y2d')
         # make sure labels came out ok
@@ -867,7 +871,7 @@ def test_2d_coord_names(self):
         self.assertEqual('x2d', ax.get_xlabel())
         self.assertEqual('y2d', ax.get_ylabel())
 
-    @slow
+    @pytest.mark.slow
     def test_levels(self):
         artist = self.plotmethod(levels=[-0.5, -0.4, 0.1])
         self.assertEqual(artist.extend, 'both')
@@ -876,7 +880,7 @@ def test_levels(self):
         self.assertEqual(artist.extend, 'neither')
 
 
-@slow
+@pytest.mark.slow
 class TestContour(Common2dMixin, PlotTestCase):
 
     plotfunc = staticmethod(xplt.contour)
@@ -906,7 +910,7 @@ def _color_as_tuple(c):
             (1.0, 1.0, 1.0))
         # the last color is now under "over"
         self.assertEqual(
-             _color_as_tuple(artist.cmap._rgba_over),
+            _color_as_tuple(artist.cmap._rgba_over),
             (0.0, 0.0, 1.0))
 
     def test_cmap_and_color_both(self):
@@ -917,7 +921,7 @@ def list_of_colors_in_cmap_deprecated(self):
         with self.assertRaises(Exception):
             self.plotmethod(cmap=['k', 'b'])
 
-    @slow
+    @pytest.mark.slow
     def test_2d_coord_names(self):
         self.plotmethod(x='x2d', y='y2d')
         # make sure labels came out ok
@@ -944,7 +948,7 @@ def test_everything_plotted(self):
         artist = self.plotmethod()
         self.assertEqual(artist.get_array().size, self.darray.size)
 
-    @slow
+    @pytest.mark.slow
     def test_2d_coord_names(self):
         self.plotmethod(x='x2d', y='y2d')
         # make sure labels came out ok
@@ -962,12 +966,13 @@ def test_dont_infer_interval_breaks_for_cartopy(self):
         # Let cartopy handle the axis limits and artist size
         self.assertTrue(artist.get_array().size <= self.darray.size)
 
-@slow
+
+@pytest.mark.slow
 class TestImshow(Common2dMixin, PlotTestCase):
 
     plotfunc = staticmethod(xplt.imshow)
 
-    @slow
+    @pytest.mark.slow
     def test_imshow_called(self):
         # Having both statements ensures the test works properly
         self.assertFalse(self.imshow_called(self.darray.plot.contourf))
@@ -982,7 +987,7 @@ def test_default_aspect_is_auto(self):
         self.darray.plot.imshow()
         self.assertEqual('auto', plt.gca().get_aspect())
 
-    @slow
+    @pytest.mark.slow
     def test_cannot_change_mpl_aspect(self):
 
         with self.assertRaisesRegexp(ValueError, 'not available in xarray'):
@@ -993,15 +998,15 @@ def test_cannot_change_mpl_aspect(self):
         self.assertEqual('auto', plt.gca().get_aspect())
         assert tuple(plt.gcf().get_size_inches()) == (10, 5)
 
-    @slow
+    @pytest.mark.slow
     def test_primitive_artist_returned(self):
         artist = self.plotmethod()
         self.assertTrue(isinstance(artist, mpl.image.AxesImage))
 
-    @slow
+    @pytest.mark.slow
     def test_seaborn_palette_needs_levels(self):
         try:
-            import seaborn
+            import seaborn  # noqa
             with self.assertRaises(ValueError):
                 self.plotmethod(cmap='husl')
         except ImportError:
@@ -1011,6 +1016,7 @@ def test_2d_coord_names(self):
         with self.assertRaisesRegexp(ValueError, 'requires 1D coordinates'):
             self.plotmethod(x='x2d', y='y2d')
 
+
 class TestFacetGrid(PlotTestCase):
 
     def setUp(self):
@@ -1019,7 +1025,7 @@ def setUp(self):
                                 coords={'z': ['a', 'b', 'c']})
         self.g = xplt.FacetGrid(self.darray, col='z')
 
-    @slow
+    @pytest.mark.slow
     def test_no_args(self):
         self.g.map_dataarray(xplt.contourf, 'x', 'y')
 
@@ -1034,7 +1040,7 @@ def test_no_args(self):
             fontsize = ax.title.get_size()
             self.assertLessEqual(fontsize, 12)
 
-    @slow
+    @pytest.mark.slow
     def test_names_appear_somewhere(self):
         self.darray.name = 'testvar'
         self.g.map_dataarray(xplt.contourf, 'x', 'y')
@@ -1046,7 +1052,7 @@ def test_names_appear_somewhere(self):
         for label in ['x', 'y']:
             self.assertIn(label, alltxt)
 
-    @slow
+    @pytest.mark.slow
     def test_text_not_super_long(self):
         self.darray.coords['z'] = [100 * letter for letter in 'abc']
         g = xplt.FacetGrid(self.darray, col='z')
@@ -1058,7 +1064,7 @@ def test_text_not_super_long(self):
         t0 = g.axes[0, 0].get_title()
         self.assertTrue(t0.endswith('...'))
 
-    @slow
+    @pytest.mark.slow
     def test_colorbar(self):
         vmin = self.darray.values.min()
         vmax = self.darray.values.max()
@@ -1072,7 +1078,7 @@ def test_colorbar(self):
 
         self.assertEqual(1, len(find_possible_colorbars()))
 
-    @slow
+    @pytest.mark.slow
     def test_empty_cell(self):
         g = xplt.FacetGrid(self.darray, col='z', col_wrap=2)
         g.map_dataarray(xplt.imshow, 'x', 'y')
@@ -1081,12 +1087,12 @@ def test_empty_cell(self):
         self.assertFalse(bottomright.has_data())
         self.assertFalse(bottomright.get_visible())
 
-    @slow
+    @pytest.mark.slow
     def test_norow_nocol_error(self):
         with self.assertRaisesRegexp(ValueError, r'[Rr]ow'):
             xplt.FacetGrid(self.darray)
 
-    @slow
+    @pytest.mark.slow
     def test_groups(self):
         self.g.map_dataarray(xplt.imshow, 'x', 'y')
         upperleft_dict = self.g.name_dicts[0, 0]
@@ -1095,19 +1101,19 @@ def test_groups(self):
 
         self.assertDataArrayEqual(upperleft_array, z0)
 
-    @slow
+    @pytest.mark.slow
     def test_float_index(self):
         self.darray.coords['z'] = [0.1, 0.2, 0.4]
         g = xplt.FacetGrid(self.darray, col='z')
         g.map_dataarray(xplt.imshow, 'x', 'y')
 
-    @slow
+    @pytest.mark.slow
     def test_nonunique_index_error(self):
         self.darray.coords['z'] = [0.1, 0.2, 0.2]
         with self.assertRaisesRegexp(ValueError, r'[Uu]nique'):
             xplt.FacetGrid(self.darray, col='z')
 
-    @slow
+    @pytest.mark.slow
     def test_robust(self):
         z = np.zeros((20, 20, 2))
         darray = DataArray(z, dims=['y', 'x', 'z'])
@@ -1129,7 +1135,7 @@ def test_robust(self):
         largest = max(abs(x) for x in numbers)
         self.assertLess(largest, 21)
 
-    @slow
+    @pytest.mark.slow
     def test_can_set_vmin_vmax(self):
         vmin, vmax = 50.0, 1000.0
         expected = np.array((vmin, vmax))
@@ -1139,14 +1145,14 @@ def test_can_set_vmin_vmax(self):
             clim = np.array(image.get_clim())
             self.assertTrue(np.allclose(expected, clim))
 
-    @slow
+    @pytest.mark.slow
     def test_can_set_norm(self):
         norm = mpl.colors.SymLogNorm(0.1)
         self.g.map_dataarray(xplt.imshow, 'x', 'y', norm=norm)
         for image in plt.gcf().findobj(mpl.image.AxesImage):
             self.assertIs(image.norm, norm)
 
-    @slow
+    @pytest.mark.slow
     def test_figure_size(self):
 
         self.assertArrayEqual(self.g.fig.get_size_inches(), (10, 3))
@@ -1169,7 +1175,7 @@ def test_figure_size(self):
         with self.assertRaisesRegexp(ValueError, "Can't use"):
             g = xplt.plot(self.darray, row=2, col='z', ax=plt.gca(), size=6)
 
-    @slow
+    @pytest.mark.slow
     def test_num_ticks(self):
         nticks = 99
         maxticks = nticks + 1
@@ -1184,12 +1190,12 @@ def test_num_ticks(self):
             self.assertGreaterEqual(xticks, nticks / 2.0)
             self.assertGreaterEqual(yticks, nticks / 2.0)
 
-    @slow
+    @pytest.mark.slow
     def test_map(self):
         self.g.map(plt.contourf, 'x', 'y', Ellipsis)
         self.g.map(lambda: None)
 
-    @slow
+    @pytest.mark.slow
     def test_map_dataset(self):
         g = xplt.FacetGrid(self.darray.to_dataset(name='foo'), col='z')
         g.map(plt.contourf, 'x', 'y', 'foo')
@@ -1208,7 +1214,7 @@ def test_map_dataset(self):
         self.assertIn('colors!', text_in_fig())
         self.assertEqual(1, len(find_possible_colorbars()))
 
-    @slow
+    @pytest.mark.slow
     def test_set_axis_labels(self):
         g = self.g.map_dataarray(xplt.contourf, 'x', 'y')
         g.set_axis_labels('longitude', 'latitude')
@@ -1216,7 +1222,7 @@ def test_set_axis_labels(self):
         for label in ['longitude', 'latitude']:
             self.assertIn(label, alltxt)
 
-    @slow
+    @pytest.mark.slow
     def test_facetgrid_colorbar(self):
         a = easy_array((10, 15, 4))
         d = DataArray(a, dims=['y', 'x', 'z'], name='foo')
@@ -1230,7 +1236,7 @@ def test_facetgrid_colorbar(self):
         d.plot.imshow(x='x', y='y', col='z', add_colorbar=False)
         self.assertEqual(0, len(find_possible_colorbars()))
 
-    @slow
+    @pytest.mark.slow
     def test_facetgrid_polar(self):
         # test if polar projection in FacetGrid does not raise an exception
         self.darray.plot.pcolormesh(col='z',
@@ -1250,7 +1256,7 @@ def setUp(self):
 
         self.darray = darray
 
-    @slow
+    @pytest.mark.slow
     def test_default_labels(self):
         g = xplt.FacetGrid(self.darray, col='col', row='row')
         self.assertEqual((2, 3), g.axes.shape)