Don't use diff's -u option. It's not portable.

Besides, with GNU diff one can use the DIFF_OPTIONS envvar.

tests/chgrp/basic

@@ -85,6 +85,6 @@ changed group of `symlink' to G1
 EOF
 
 cmp expected actual \
-  || { diff -u expected actual 1>&2; fail=1; }
+  || { diff expected actual 1>&2; fail=1; }
 
 (exit $fail); exit

tests/ls/no-arg

@@ -35,7 +35,7 @@ fail=0
 ls > out || fail=1
 
 cmp out exp || fail=1
-test $fail = 1 && diff -u out exp 2> /dev/null
+test $fail = 1 && diff out exp 2> /dev/null
 
 cat > exp <<\EOF
 .:
@@ -54,6 +54,6 @@ EOF
 ls -R > out || fail=1
 
 cmp out exp || fail=1
-test $fail = 1 && diff -u out exp 2> /dev/null
+test $fail = 1 && diff out exp 2> /dev/null
 
 (exit $fail); exit

tests/ls/recursive

@@ -50,7 +50,7 @@ c:
 EOF
 
 cmp out exp || fail=1
-test $fail = 1 && diff -u out exp 2> /dev/null
+test $fail = 1 && diff out exp 2> /dev/null
 
 rm -rf out exp
 ls -R1 x y f > out || fail=1
@@ -63,6 +63,6 @@ y:
 EOF
 
 cmp out exp || fail=1
-test $fail = 1 && diff -u out exp 2> /dev/null
+test $fail = 1 && diff out exp 2> /dev/null
 
 (exit $fail); exit

tests/ls/rt-1

@@ -39,7 +39,7 @@ b
 c
 EOF
 cmp out exp || fail=1
-test $fail = 1 && diff -u out exp 2> /dev/null
+test $fail = 1 && diff out exp 2> /dev/null
 
 rm -rf out exp
 ls -1rt a b c > out || fail=1
@@ -49,6 +49,6 @@ b
 a
 EOF
 cmp out exp || fail=1
-test $fail = 1 && diff -u out exp 2> /dev/null
+test $fail = 1 && diff out exp 2> /dev/null
 
 (exit $fail); exit