adding tests and changing typecasts

Author: xtanion

lib/matplotlib/contour.py

@@ -1452,7 +1452,7 @@ def _contour_args(self, args, kwargs):
         if self.logscale and self.zmin <= 0:
             z = ma.masked_where(z <= 0, z)
             _api.warn_external('Log scale: values of z <= 0 have been masked')
-            self.zmin = float(z.min())
+            self.zmin = z.min().astype(float)
         self._process_contour_level_args(args, z.dtype)
         return (x, y, z)
 

lib/matplotlib/tests/test_contour.py

@@ -715,3 +715,9 @@ def test_bool_autolevel():
     assert plt.tricontour(x, y, z).levels.tolist() == [.5]
     assert plt.tricontourf(x, y, z.tolist()).levels.tolist() == [0, .5, 1]
     assert plt.tricontourf(x, y, z).levels.tolist() == [0, .5, 1]
+
+def test_all_nan():
+    x = np.array([[np.nan, np.nan], [np.nan, np.nan]])
+    assert_array_almost_equal(plt.contour(x).levels.tolist(),
+                              [-1e-13, -7.5e-14, -5e-14, -2.4e-14, 0.0,
+                                2.4e-14, 5e-14, 7.5e-14, 1e-13])