diff --git a/tests/blackbox-readonly-dispatch.py b/tests/blackbox-readonly-dispatch.py
--- a/tests/blackbox-readonly-dispatch.py
+++ b/tests/blackbox-readonly-dispatch.py
@@ -11,28 +11,28 @@ def testdispatch(cmd):
     Prints command and result value, but does not handle quoting.
     """
     ui = uimod.ui.load()
-    ui.status("running: %s\n" % cmd)
+    ui.status(b"running: %s\n" % cmd)
     req = dispatch.request(cmd.split(), ui)
     result = dispatch.dispatch(req)
-    ui.status("result: %r\n" % result)
+    ui.status(b"result: %r\n" % result)
 
 # create file 'foo', add and commit
-f = open('foo', 'wb')
-f.write('foo\n')
+f = open(b'foo', 'wb')
+f.write(b'foo\n')
 f.close()
-testdispatch("--debug add foo")
-testdispatch("--debug commit -m commit1 -d 2000-01-01 foo")
+testdispatch(b"--debug add foo")
+testdispatch(b"--debug commit -m commit1 -d 2000-01-01 foo")
 
 # append to file 'foo' and commit
-f = open('foo', 'ab')
-f.write('bar\n')
+f = open(b'foo', 'ab')
+f.write(b'bar\n')
 f.close()
 # remove blackbox.log directory (proxy for readonly log file)
-os.rmdir(".hg/blackbox.log")
+os.rmdir(b".hg/blackbox.log")
 # replace it with the real blackbox.log file
-os.rename(".hg/blackbox.log-", ".hg/blackbox.log")
-testdispatch("--debug commit -m commit2 -d 2000-01-02 foo")
+os.rename(b".hg/blackbox.log-", b".hg/blackbox.log")
+testdispatch(b"--debug commit -m commit2 -d 2000-01-02 foo")
 
 # check 88803a69b24 (fancyopts modified command table)
-testdispatch("--debug log -r 0")
-testdispatch("--debug log -r tip")
+testdispatch(b"--debug log -r 0")
+testdispatch(b"--debug log -r tip")