Don't require a diff which accepts the -N option.
--- a/tests/test-extdiff Fri Dec 01 22:09:05 2006 +0100
+++ b/tests/test-extdiff Fri Dec 01 22:29:47 2006 +0100
@@ -7,11 +7,7 @@
cd a
echo a > a
hg add
-diff -N /dev/null /dev/null 2> /dev/null
-if [ $? -ne 0 ]; then
- opt="-p gdiff"
-fi
-hg extdiff -o -Nr $opt
+hg extdiff -o -r $opt
echo "[extdiff]" >> $HGRCPATH
echo "cmd.falabala=echo" >> $HGRCPATH
--- a/tests/test-extdiff.out Fri Dec 01 22:09:05 2006 +0100
+++ b/tests/test-extdiff.out Fri Dec 01 22:29:47 2006 +0100
@@ -1,9 +1,7 @@
adding a
making snapshot of 0 files from rev 000000000000
making snapshot of 1 files from working dir
-diff -Nr a.000000000000/a a/a
-0a1
-> a
+Only in a: a
making snapshot of 0 files from rev 000000000000
making snapshot of 1 files from working dir
diffing a.000000000000 a