TST: Also output the actual error on svg backend tests using subprocess

jankatins · jankatins · commit 45a1d22aa552 · 2016-07-15T17:58:55.000+02:00
Up to now the tests only checked the returncode of a test invoking subprocess,
but didn't show the real error printed by the failing tests.

Now we show print the original output on failure so that it is shown in the test
output.
diff --git a/lib/matplotlib/tests/test_backend_svg.py b/lib/matplotlib/tests/test_backend_svg.py
@@ -153,16 +153,25 @@ def _test_determinism_save(filename, usetex):
 def _test_determinism(filename, usetex):
     import os
     import sys
-    from subprocess import check_call
+    from subprocess import check_output, STDOUT, CalledProcessError
     from nose.tools import assert_equal
     plots = []
     for i in range(3):
-        check_call([sys.executable, '-R', '-c',
-                    'import matplotlib; '
-                    'matplotlib.use("svg"); '
-                    'from matplotlib.tests.test_backend_svg '
-                    'import _test_determinism_save;'
-                    '_test_determinism_save(%r, %r)' % (filename, usetex)])
+        # Using check_output and setting stderr to STDOUT will capture the real
+        # problem in the output property of the exception
+        try:
+            check_output([sys.executable, '-R', '-c',
+                        'import matplotlib; '
+                        'matplotlib.use("svg"); '
+                        'from matplotlib.tests.test_backend_svg '
+                        'import _test_determinism_save;'
+                        '_test_determinism_save(%r, %r)' % (filename, usetex)],
+                        stderr=STDOUT)
+        except CalledProcessError as e:
+            # it's easier to use utf8 and ask for forgiveness than try to figure
+            # out what the current console has as an encoding :-/
+            print(e.output.decode(encoding="utf-8", errors="ignore"))
+            raise e
         with open(filename, 'rb') as fd:
             plots.append(fd.read())
         os.unlink(filename)
