This bug similar to #3329. I have a problem running tests on solaris 10 using samba 3.0.22. I checked SAMBA_3_0 branch and found that runtests.sh is now named selftest.sh but it inherited at least 2 bugs from its ancestor:

--- selftest.sh 2006-04-21 13:10:51.599041750 +0800
+++ selftest.sh.fixed   2006-04-21 13:44:32.505340500 +0800
@@ -15,7 +15,7 @@
 mkdir -p $PREFIX || exit $?
 OLD_PWD=`pwd`
 cd $PREFIX || exit $?
-export PREFIX_ABS=`pwd`
+PREFIX_ABS=`pwd`
 cd $OLD_PWD

 if [ -z "$TORTURE_MAXTIME" ]; then
@@ -29,7 +29,7 @@

 SERVER=localhost2
 SERVER_IP=127.0.0.2
-USERNAME=`whoami`
+USERNAME=`PATH=/usr/ucb:$PATH whoami`
 PASSWORD=test

 SRCDIR=`pwd`

First, this syntax confeses sh. PREFIX_ABS is still exported latter. 
Second, whoami on solaris is in /usr/ucb dir and this dir not in the PATH by default. This should work on any sh-like shell.