diff -r f8154ddaaed3 -r d6b6f1b441cf tests/run-tests.py
--- a/tests/run-tests.py	Fri Oct 19 01:52:16 2018 +0200
+++ b/tests/run-tests.py	Thu Nov 01 14:29:21 2018 +0100
@@ -1078,7 +1078,6 @@
                                                    b'daemon.pids'))
         env["HGEDITOR"] = ('"' + sys.executable + '"'
                            + ' -c "import sys; sys.exit(0)"')
-        env["HGMERGE"] = "internal:merge"
         env["HGUSER"]   = "test"
         env["HGENCODING"] = "ascii"
         env["HGENCODINGMODE"] = "strict"
@@ -1116,6 +1115,7 @@
             'EDITOR',
             'GREP_OPTIONS',
             'HG',
+            'HGMERGE',
             'HGPLAIN',
             'HGPLAINEXCEPT',
             'HGPROF',
@@ -1146,6 +1146,7 @@
             hgrc.write(b'[ui]\n')
             hgrc.write(b'slash = True\n')
             hgrc.write(b'interactive = False\n')
+            hgrc.write(b'merge = internal:merge\n')
             hgrc.write(b'mergemarkers = detailed\n')
             hgrc.write(b'promptecho = True\n')
             hgrc.write(b'[defaults]\n')