Use a default pam configuration using pam_unix sha512 option.

tests/passwd/20_passwd_user_change_password_same_user/config/etc/pam.d/common-password

@@ -0,0 +1,33 @@
+#
+# /etc/pam.d/common-password - password-related modules common to all services
+#
+# This file is included from other service-specific PAM config files,
+# and should contain a list of modules that define the services to be
+# used to change user passwords.  The default is pam_unix.
+
+# Explanation of pam_unix options:
+#
+# The "sha512" option enables salted SHA512 passwords.  Without this option,
+# the default is Unix crypt.  Prior releases used the option "md5".
+#
+# The "obscure" option replaces the old `OBSCURE_CHECKS_ENAB' option in
+# login.defs.
+#
+# See the pam_unix manpage for other options.
+
+# As of pam 1.0.1-6, this file is managed by pam-auth-update by default.
+# To take advantage of this, it is recommended that you configure any
+# local modules either before or after the default block, and use
+# pam-auth-update to manage selection of other modules.  See
+# pam-auth-update(8) for details.
+
+# here are the per-package modules (the "Primary" block)
+password	[success=1 default=ignore]	pam_unix.so obscure sha512
+# here's the fallback if no module succeeds
+password	requisite			pam_deny.so
+# prime the stack with a positive return value if there isn't one already;
+# this avoids us returning an error just because nothing sets a success code
+# since the modules above will each just jump around
+password	required			pam_permit.so
+# and here are more per-package modules (the "Additional" block)
+# end of pam-auth-update config

tests/passwd/20_passwd_user_change_password_same_user/data/shadow

@@ -17,4 +17,4 @@ irc:*:12977:0:99999:7:::
 gnats:*:12977:0:99999:7:::
 nobody:*:12977:0:99999:7:::
 Debian-exim:!:12977:0:99999:7:::
-foo:@PASS_MD5 password-foo@:@TODAY@:0:99999:7:::
+foo:@PASS_SHA512 password-foo@:@TODAY@:0:99999:7:::