Added mplot3d tests in mpl_toolkits.tests

- This complements PR matplotlib#2135
- Also tests issue matplotlib#1933, which was fixed but untested
- Also changes the remove_text decorator,
  to remove text on the z-axis.

lib/matplotlib/testing/decorators.py

@@ -110,6 +110,11 @@ def remove_text(figure):
             ax.xaxis.set_minor_formatter(ticker.NullFormatter())
             ax.yaxis.set_major_formatter(ticker.NullFormatter())
             ax.yaxis.set_minor_formatter(ticker.NullFormatter())
+            try:
+                ax.zaxis.set_major_formatter(ticker.NullFormatter())
+                ax.zaxis.set_minor_formatter(ticker.NullFormatter())
+            except AttributeError:
+                pass
 
     def test(self):
         baseline_dir, result_dir = _image_directories(self._func)

lib/matplotlib/tests/test_backend_pdf.py

@@ -1,6 +1,10 @@
 # -*- encoding: utf-8 -*-
 
-from matplotlib import rcParams
+import io
+
+import numpy as np
+
+from matplotlib import cm, rcParams
 from matplotlib import pyplot as plt
 from matplotlib.testing.decorators import image_comparison, knownfailureif, cleanup
 
@@ -26,8 +30,6 @@ def test_use14corefonts():
 
 @cleanup
 def test_type42():
-    import io
-
     rcParams['pdf.fonttype'] = 42
 
     fig = plt.figure()