--- ./tests/test_cmdline.py.orig	2019-01-17 21:11:36.245282362 +0100
+++ ./tests/test_cmdline.py	2019-01-17 21:44:28.090657851 +0100
@@ -28,10 +28,37 @@
 '''
 
 
+class StrictStringOutput(StringIO):
+    log = sys.stderr
+
+    def __init__(self):
+        StringIO.__init__(self)
+        self.__text_type = None
+        self.__text_sample = None
+
+    def write(self, s):
+        return StringIO.write(self, self.__validate(s))
+
+    def writelines(self, iterable):
+        return StringIO.writelines(self.__validate(text) for text in iterable)
+
+    def __validate(self, text):
+        if self.__text_type is None:
+            self.__text_type = text.__class__
+            self.__text_sample = text
+        elif text.__class__ != self.__text_type:
+            self.log.write(
+                    "Incompatible types %r (%s) and %r (%s)\n" % (
+                        self.__text_sample, self.__text_type,
+                        text, text.__class__))
+        return text
+
+
 def run_cmdline(*args, **kwds):
     saved_stdin = sys.stdin
     saved_stdout = sys.stdout
     saved_stderr = sys.stderr
+    print(sys.version_info)
     if sys.version_info > (3,):
         stdin_buffer = BytesIO()
         stdout_buffer = BytesIO()
@@ -40,9 +67,9 @@
         new_stdout = sys.stdout = io.TextIOWrapper(stdout_buffer, 'utf-8')
         new_stderr = sys.stderr = io.TextIOWrapper(stderr_buffer, 'utf-8')
     else:
-        stdin_buffer = new_stdin = sys.stdin = StringIO()
-        stdout_buffer = new_stdout = sys.stdout = StringIO()
-        stderr_buffer = new_stderr = sys.stderr = StringIO()
+        stdin_buffer = new_stdin = sys.stdin = StrictStringOutput()
+        stdout_buffer = new_stdout = sys.stdout = StrictStringOutput()
+        stderr_buffer = new_stderr = sys.stderr = StrictStringOutput()
     new_stdin.write(kwds.get('stdin', ''))
     new_stdin.seek(0, 0)
     try:
@@ -53,8 +80,9 @@
         sys.stderr = saved_stderr
     new_stdout.flush()
     new_stderr.flush()
-    out, err = stdout_buffer.getvalue().decode('utf-8'), \
-        stderr_buffer.getvalue().decode('utf-8')
+    print(repr(stdout_buffer.buflist))
+    out = stdout_buffer.getvalue().decode('utf-8')
+    err = stderr_buffer.getvalue().decode('utf-8')
     return (ret, out, err)
 
 
--- ./tests/test_util.py.orig	2019-01-17 21:15:08.341082845 +0100
+++ ./tests/test_util.py	2019-01-17 21:32:47.646780336 +0100
@@ -10,7 +10,7 @@
 import re
 import unittest
 
-from pygments import util, console
+from pygments import util, console, StringIO
 
 
 class FakeLexer(object):
@@ -211,3 +211,24 @@
         self.assertEqual(console.reset_color(), console.codes['reset'])
         self.assertEqual(console.colorize('blue', 'text'),
                          console.codes['blue'] + 'text' + console.codes['reset'])
+
+
+class StringIOTest(unittest.TestCase):
+
+    def test_mix_default_unicode(self):
+        buf = StringIO()
+        buf.write('The Arduino\xc2\xae language style')
+        buf.write(u'unicode')
+        buf.getvalue()
+
+    def test_mix_default_bytes(self):
+        buf = StringIO()
+        buf.write(u'The Arduino\xc2\xae language style')
+        buf.write(b'bytes')
+        buf.getvalue()
+
+    def test_mix_unicode_bytes(self):
+        buf = StringIO()
+        buf.write('The Arduino\xc2\xae language style')
+        buf.write(b'bytes \xc2\xae')
+        buf.getvalue()