tests: port test-ui-color.py to Python 3

As in some other tests, I like confirming that we're dealing with
bytes here, so the b prefix is now in the expected output on both 2
and 3.

Differential Revision: https://phab.mercurial-scm.org/D3512

contrib/python3-whitelist

@@ -450,6 +450,7 b' test-tag.t'
 test-tags.t
 test-template-engine.t
 test-treemanifest.t
+test-ui-color.py
 test-unamend.t
 test-uncommit.t
 test-unified-test.t

tests/test-ui-color.py

@@ -5,6 +5,9 b' from mercurial import ('
     dispatch,
     ui as uimod,
 )
+from mercurial.utils import (
+    stringutil,
+)
 
 # ensure errors aren't buffered
 testui = uimod.ui()
@@ -12,7 +15,7 b' testui.pushbuffer()'
 testui.write((b'buffered\n'))
 testui.warn((b'warning\n'))
 testui.write_err(b'error\n')
-print(repr(testui.popbuffer()))
+print(stringutil.pprint(testui.popbuffer()).decode('ascii'))
 
 # test dispatch.dispatch with the same ui object
 hgrc = open(os.environ["HGRCPATH"], 'wb')
@@ -35,4 +38,3 b' runcmd()'
 print("colored? %s" % (ui_._colormode is not None))
 runcmd()
 print("colored? %s" % (ui_._colormode is not None))
-

tests/test-ui-color.py.out

@@ -1,5 +1,5 b''
 warning
 error
-'buffered\n'
+b'buffered\n'
 colored? True
 colored? True