diff --git a/lib/matplotlib/backends/backend_agg.py b/lib/matplotlib/backends/backend_agg.py
index c4d93d9a9a89..fd262c2bb710 100644
--- a/lib/matplotlib/backends/backend_agg.py
+++ b/lib/matplotlib/backends/backend_agg.py
@@ -356,7 +356,7 @@ def post_processing(image, dpi):
         self._update_methods()
 
         if w > 0 and h > 0:
-            img = np.fromstring(buffer, np.uint8)
+            img = np.frombuffer(buffer, np.uint8)
             img, ox, oy = post_processing(img.reshape((h, w, 4)) / 255.,
                                           self.dpi)
             gc = self.new_gc()
diff --git a/lib/matplotlib/dates.py b/lib/matplotlib/dates.py
index a229e09f5e63..41f78ca98abb 100644
--- a/lib/matplotlib/dates.py
+++ b/lib/matplotlib/dates.py
@@ -1348,10 +1348,9 @@ def get_locator(self, dmin, dmax):
         else:
             locator = MicrosecondLocator(interval, tz=self.tz)
             if dmin.year > 20 and interval < 1000:
-                _log.warn('Plotting microsecond time intervals is not'
-                          ' well supported. Please see the'
-                          ' MicrosecondLocator documentation'
-                          ' for details.')
+                _log.warning('Plotting microsecond time intervals is not well '
+                             'supported. Please see the MicrosecondLocator '
+                             'documentation for details.')
 
         locator.set_axis(self.axis)
 
diff --git a/lib/matplotlib/image.py b/lib/matplotlib/image.py
index b9f5d5ae4930..1641bac9cc0e 100644
--- a/lib/matplotlib/image.py
+++ b/lib/matplotlib/image.py
@@ -1460,9 +1460,9 @@ def pil_to_array(pilImage):
         # return MxN luminance array of uint16
         raw = pilImage.tobytes('raw', pilImage.mode)
         if pilImage.mode.endswith('B'):
-            x = np.fromstring(raw, '>u2')
+            x = np.frombuffer(raw, '>u2')
         else:
-            x = np.fromstring(raw, '<u2')
+            x = np.frombuffer(raw, '<u2')
         return x.reshape(pilImage.size[::-1]).astype('=u2')
     else:  # try to convert to an rgba image
         try:
diff --git a/lib/matplotlib/testing/decorators.py b/lib/matplotlib/testing/decorators.py
index cddb910e12fa..d606a9666999 100644
--- a/lib/matplotlib/testing/decorators.py
+++ b/lib/matplotlib/testing/decorators.py
@@ -158,15 +158,25 @@ def _xfail_if_format_is_uncomparable(extension):
 
 def _mark_xfail_if_format_is_uncomparable(extension):
     if isinstance(extension, str):
-        will_fail = extension not in comparable_formats()
+        name = extension
+        marks = []
+    elif isinstance(extension, tuple):
+        # Extension might be a pytest ParameterSet instead of a plain string.
+        # Unfortunately, this type is not exposed, so since it's a namedtuple,
+        # check for a tuple instead.
+        name = extension.values[0]
+        marks = list(extension.marks)
     else:
         # Extension might be a pytest marker instead of a plain string.
-        will_fail = extension.args[0] not in comparable_formats()
-    if will_fail:
-        fail_msg = 'Cannot compare %s files on this system' % extension
+        name = extension.args[0]
+        marks = [extension.mark]
+
+    if name not in comparable_formats():
+        fail_msg = 'Cannot compare %s files on this system' % (name, )
         import pytest
-        return pytest.mark.xfail(extension, reason=fail_msg, strict=False,
-                                 raises=ImageComparisonFailure)
+        marks += [pytest.mark.xfail(reason=fail_msg, strict=False,
+                                    raises=ImageComparisonFailure)]
+        return pytest.param(name, marks=marks)
     else:
         return extension
 
diff --git a/lib/matplotlib/tests/test_backend_pdf.py b/lib/matplotlib/tests/test_backend_pdf.py
index a0bfe6213e73..04102640ff7b 100644
--- a/lib/matplotlib/tests/test_backend_pdf.py
+++ b/lib/matplotlib/tests/test_backend_pdf.py
@@ -2,6 +2,7 @@
 import os
 import sys
 import tempfile
+import warnings
 
 import numpy as np
 import pytest
@@ -14,9 +15,11 @@
                                             _determinism_check)
 
 
-needs_usetex = pytest.mark.skipif(
-    not checkdep_usetex(True),
-    reason="This test needs a TeX installation")
+with warnings.catch_warnings():
+    warnings.simplefilter('ignore')
+    needs_usetex = pytest.mark.skipif(
+        not checkdep_usetex(True),
+        reason="This test needs a TeX installation")
 
 
 @image_comparison(baseline_images=['pdf_use14corefonts'],
diff --git a/lib/matplotlib/tests/test_backend_ps.py b/lib/matplotlib/tests/test_backend_ps.py
index dfa4747ae518..a8237f77f094 100644
--- a/lib/matplotlib/tests/test_backend_ps.py
+++ b/lib/matplotlib/tests/test_backend_ps.py
@@ -3,6 +3,7 @@
 from pathlib import Path
 import re
 import tempfile
+import warnings
 
 import pytest
 
@@ -14,12 +15,14 @@
                                             _determinism_check)
 
 
-needs_ghostscript = pytest.mark.skipif(
-    matplotlib.checkdep_ghostscript()[0] is None,
-    reason="This test needs a ghostscript installation")
-needs_usetex = pytest.mark.skipif(
-    not matplotlib.checkdep_usetex(True),
-    reason="This test needs a TeX installation")
+with warnings.catch_warnings():
+    warnings.simplefilter('ignore')
+    needs_ghostscript = pytest.mark.skipif(
+        matplotlib.checkdep_ghostscript()[0] is None,
+        reason="This test needs a ghostscript installation")
+    needs_usetex = pytest.mark.skipif(
+        not matplotlib.checkdep_usetex(True),
+        reason="This test needs a TeX installation")
 
 
 # This tests tends to hit a TeX cache lock on AppVeyor.
diff --git a/lib/matplotlib/tests/test_backend_svg.py b/lib/matplotlib/tests/test_backend_svg.py
index 1c06821841cb..9fce1fa84d68 100644
--- a/lib/matplotlib/tests/test_backend_svg.py
+++ b/lib/matplotlib/tests/test_backend_svg.py
@@ -2,6 +2,7 @@
 from io import BytesIO
 import os
 import tempfile
+import warnings
 import xml.parsers.expat
 
 import pytest
@@ -12,9 +13,11 @@
 from matplotlib import dviread
 
 
-needs_usetex = pytest.mark.skipif(
-    not matplotlib.checkdep_usetex(True),
-    reason="This test needs a TeX installation")
+with warnings.catch_warnings():
+    warnings.simplefilter('ignore')
+    needs_usetex = pytest.mark.skipif(
+        not matplotlib.checkdep_usetex(True),
+        reason="This test needs a TeX installation")
 
 
 def test_visibility():
diff --git a/lib/matplotlib/tests/test_mathtext.py b/lib/matplotlib/tests/test_mathtext.py
index a05c8b3c8977..fd6cebe1fc54 100644
--- a/lib/matplotlib/tests/test_mathtext.py
+++ b/lib/matplotlib/tests/test_mathtext.py
@@ -267,7 +267,7 @@ def test_single_minus_sign():
 
     buff = io.BytesIO()
     plt.savefig(buff, format="rgba", dpi=1000)
-    array = np.fromstring(buff.getvalue(), dtype=np.uint8)
+    array = np.frombuffer(buff.getvalue(), dtype=np.uint8)
 
     # If this fails, it would be all white
     assert not np.all(array == 0xff)
diff --git a/lib/matplotlib/tests/test_simplification.py b/lib/matplotlib/tests/test_simplification.py
index 1f0a8d76e63e..5d86e42e2fe5 100644
--- a/lib/matplotlib/tests/test_simplification.py
+++ b/lib/matplotlib/tests/test_simplification.py
@@ -264,7 +264,7 @@ def test_start_with_moveto():
 AABHqP//ej8AAD6z//+FPwAANb7//48/AAAsyf//lz8AACPU//+ePwAAGt///6M/AAAR6v//pj8A
 AAj1//+nPwAA/////w=="""
 
-    verts = np.fromstring(base64.decodebytes(data), dtype='<i4')
+    verts = np.frombuffer(base64.decodebytes(data), dtype='<i4')
     verts = verts.reshape((len(verts) // 2, 2))
     path = Path(verts)
     segs = path.iter_segments(transforms.IdentityTransform(),
diff --git a/lib/matplotlib/tests/test_text.py b/lib/matplotlib/tests/test_text.py
index 17e33698fd36..19e00be77c5b 100644
--- a/lib/matplotlib/tests/test_text.py
+++ b/lib/matplotlib/tests/test_text.py
@@ -11,9 +11,11 @@
 from matplotlib.testing.decorators import image_comparison
 
 
-needs_usetex = pytest.mark.skipif(
-    not matplotlib.checkdep_usetex(True),
-    reason="This test needs a TeX installation")
+with warnings.catch_warnings():
+    warnings.simplefilter('ignore')
+    needs_usetex = pytest.mark.skipif(
+        not matplotlib.checkdep_usetex(True),
+        reason="This test needs a TeX installation")
 
 
 @image_comparison(baseline_images=['font_styles'])
@@ -134,8 +136,8 @@ def test_multiline2():
     ax.set_xlim([0, 1.4])
     ax.set_ylim([0, 2])
     ax.axhline(0.5, color='C2', linewidth=0.3)
-    sts = ['Line', '2 Lineg\n 2 Lg', '$\sum_i x $', 'hi $\sum_i x $\ntest',
-           'test\n $\sum_i x $', '$\sum_i x $\n $\sum_i x $']
+    sts = ['Line', '2 Lineg\n 2 Lg', '$\\sum_i x $', 'hi $\\sum_i x $\ntest',
+           'test\n $\\sum_i x $', '$\\sum_i x $\n $\\sum_i x $']
     renderer = fig.canvas.get_renderer()
 
     def draw_box(ax, tt):
diff --git a/lib/matplotlib/tests/test_usetex.py b/lib/matplotlib/tests/test_usetex.py
index ebdb6a726de4..644493279d30 100644
--- a/lib/matplotlib/tests/test_usetex.py
+++ b/lib/matplotlib/tests/test_usetex.py
@@ -1,3 +1,5 @@
+import warnings
+
 import pytest
 
 import matplotlib
@@ -5,8 +7,14 @@
 import matplotlib.pyplot as plt
 
 
-@pytest.mark.skipif(not matplotlib.checkdep_usetex(True),
-                    reason='Missing TeX or Ghostscript or dvipng')
+with warnings.catch_warnings():
+    warnings.simplefilter('ignore')
+    needs_usetex = pytest.mark.skipif(
+        not matplotlib.checkdep_usetex(True),
+        reason='Missing TeX of Ghostscript or dvipng')
+
+
+@needs_usetex
 @image_comparison(baseline_images=['test_usetex'],
                   extensions=['pdf', 'png'],
                   tol=0.3)
diff --git a/lib/mpl_toolkits/tests/test_mplot3d.py b/lib/mpl_toolkits/tests/test_mplot3d.py
index 908de75777a1..880553d8882c 100644
--- a/lib/mpl_toolkits/tests/test_mplot3d.py
+++ b/lib/mpl_toolkits/tests/test_mplot3d.py
@@ -133,9 +133,10 @@ def test_lines3d():
 
 
 # Reason for flakiness of SVG test is still unknown.
-@image_comparison(baseline_images=['mixedsubplot'], remove_text=True,
-                  extensions=['png', 'pdf',
-                              pytest.mark.xfail('svg', strict=False)])
+@image_comparison(
+    baseline_images=['mixedsubplot'], remove_text=True,
+    extensions=['png', 'pdf',
+                pytest.param('svg', marks=pytest.mark.xfail(strict=False))])
 def test_mixedsubplots():
     def f(t):
         s1 = np.cos(2*np.pi*t)