diff --git a/t/001-deb-systemd-helper.t b/t/001-deb-systemd-helper.t
index ed661c8..01e2984 100644
--- a/t/001-deb-systemd-helper.t
+++ b/t/001-deb-systemd-helper.t
@@ -18,17 +18,20 @@ use Linux::Clone; # neither in core nor in Debian :-/
 
 my $dsh = "$FindBin::Bin/../script/deb-systemd-helper";
 
-sub _unit_enabled {
-    my ($unit_file, $cb, $verb) = @_;
+sub _unit_check {
+    my ($unit_file, $cmd, $cb, $verb) = @_;
 
-    my $retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh is-enabled $unit_file");
+    my $retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh $cmd $unit_file");
     isnt($retval, -1, 'deb-systemd-helper could be executed');
     ok(!($retval & 127), 'deb-systemd-helper did not exit due to a signal');
-    $cb->($retval >> 8, 0, "random unit file $verb enabled");
+    $cb->($retval >> 8, 0, "random unit file $verb $cmd");
 }
 
-sub is_enabled { _unit_enabled($_[0], \&is, 'is') }
-sub isnt_enabled { _unit_enabled($_[0], \&isnt, 'isnt') }
+sub is_enabled { _unit_check($_[0], 'is-enabled', \&is, 'is') }
+sub isnt_enabled { _unit_check($_[0], 'is-enabled', \&isnt, 'isnt') }
+
+sub is_debian_installed { _unit_check($_[0], 'debian-installed', \&is, 'is') }
+sub isnt_debian_installed { _unit_check($_[0], 'debian-installed', \&isnt, 'isnt') }
 
 my $retval = Linux::Clone::unshare Linux::Clone::NEWNS;
 BAIL_OUT("Cannot unshare(NEWNS): $!") if $retval != 0;
@@ -57,6 +60,7 @@ close($fh);
 $random_unit = basename($random_unit);
 
 isnt_enabled($random_unit);
+isnt_debian_installed($random_unit);
 
 # ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
 # ┃ Verify “is-enabled” is not true for a random, existing unit file.         ┃
@@ -78,6 +82,7 @@ EOT
 close($fh);
 
 isnt_enabled($random_unit);
+isnt_debian_installed($random_unit);
 
 # ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
 # ┃ Verify “enable” creates the requested symlinks.                           ┃
@@ -97,6 +102,7 @@ is(readlink($symlink_path), $servicefile_path,
 # ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
 
 is_enabled($random_unit);
+is_debian_installed($random_unit);
 
 # ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
 # ┃ Verify deleting the symlinks and running “enable” again does not          ┃
@@ -106,6 +112,7 @@ is_enabled($random_unit);
 unlink($symlink_path);
 ok(! -l $symlink_path, 'symlink deleted');
 isnt_enabled($random_unit);
+is_debian_installed($random_unit);
 
 $retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh enable $random_unit");
 
@@ -122,6 +129,7 @@ ok(-f $statefile, 'state file exists');
 $retval = system("DPKG_MAINTSCRIPT_PACKAGE=test _DEB_SYSTEMD_HELPER_PURGE=1 $dsh disable $random_unit");
 
 ok(! -f $statefile, 'state file does not exist anymore after purging');
+isnt_debian_installed($random_unit);
 
 # ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
 # ┃ Verify “enable” after purging does re-create the symlinks.                ┃
@@ -133,5 +141,6 @@ isnt_enabled($random_unit);
 $retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh enable $random_unit");
 
 is_enabled($random_unit);
+is_debian_installed($random_unit);
 
 done_testing;
diff --git a/t/002-deb-systemd-helper-update.t b/t/002-deb-systemd-helper-update.t
index 97621d2..ae401e9 100644
--- a/t/002-deb-systemd-helper-update.t
+++ b/t/002-deb-systemd-helper-update.t
@@ -105,7 +105,7 @@ is_enabled($random_unit);
 # ┃ Modify the unit file and verify that “is-enabled” is no longer true.      ┃
 # ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
 
-open($fh, '>', $servicefile_path);
+open($fh, '>>', $servicefile_path);
 print $fh "Alias=newalias.service\n";
 close($fh);
 
@@ -152,4 +152,86 @@ is_deeply(
     [ $symlink_path, $new_symlink_path ],
     'state file updated');
 
+# ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+# ┃ Modify the unit file and verify that “is-enabled” is no longer true.      ┃
+# ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+open($fh, '>>', $servicefile_path);
+print $fh "Alias=another.service\n";
+close($fh);
+
+isnt_enabled($random_unit);
+
+# ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+# ┃ Verify “was-enabled” is still true (operates on the state file).          ┃
+# ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+$retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh was-enabled $random_unit");
+isnt($retval, -1, 'deb-systemd-helper could be executed');
+ok(!($retval & 127), 'deb-systemd-helper did not exit due to a signal');
+is($retval >> 8, 0, "random unit file was-enabled");
+
+# ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+# ┃ Verify the new symlink is not yet in the state file.                      ┃
+# ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+is_deeply(
+    [ state_file_entries($statefile) ],
+    [ $symlink_path, $new_symlink_path ],
+    'state file does not contain the new link yet');
+
+# ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+# ┃ Verify “update-state” does not create the symlink, but records it in the  ┃
+# ┃ state file.                                                               ┃
+# ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+my $new_symlink_path2 = '/etc/systemd/system/another.service';
+ok(! -l $new_symlink_path2, 'new symlink does not exist yet');
+
+$retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh update-state $random_unit");
+ok(! -l $new_symlink_path2, 'new symlink still does not exist');
+
+isnt_enabled($random_unit);
+
+is_deeply(
+    [ state_file_entries($statefile) ],
+    [ $symlink_path, $new_symlink_path, $new_symlink_path2 ],
+    'state file updated');
+
+# ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+# ┃ Rewrite the original contents and verify “update-state” removes the old   ┃
+# ┃ links that are no longer present.                                         ┃
+# ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+open($fh, '>', $servicefile_path);
+print $fh <<'EOT';
+[Unit]
+Description=test unit
+
+[Service]
+ExecStart=/bin/sleep 1
+
+[Install]
+WantedBy=multi-user.target
+EOT
+close($fh);
+
+unlink($new_symlink_path);
+
+ok(! -l $new_symlink_path, 'new symlink still does not exist');
+ok(! -l $new_symlink_path2, 'new symlink 2 still does not exist');
+
+$retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh update-state $random_unit");
+
+ok(! -l $new_symlink_path, 'new symlink still does not exist');
+ok(! -l $new_symlink_path2, 'new symlink 2 still does not exist');
+
+is_enabled($random_unit);
+
+is_deeply(
+    [ state_file_entries($statefile) ],
+    [ $symlink_path ],
+    'state file updated');
+
+
 done_testing;
diff --git a/t/003-deb-systemd-helper-complex.t b/t/003-deb-systemd-helper-complex.t
new file mode 100644
index 0000000..924013a
--- /dev/null
+++ b/t/003-deb-systemd-helper-complex.t
@@ -0,0 +1,142 @@
+#!perl
+# vim:ts=4:sw=4:et
+
+use strict;
+use warnings;
+use Test::More;
+use File::Temp qw(tempfile tempdir); # in core since perl 5.6.1
+use File::Path qw(make_path); # in core since Perl 5.001
+use File::Basename; # in core since Perl 5
+use FindBin; # in core since Perl 5.00307
+use Linux::Clone; # neither in core nor in Debian :-/
+
+# ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+# ┃ SETUP: in a new mount namespace, bindmount tmpdirs on /etc/systemd and    ┃
+# ┃ /var/lib/systemd to start with clean directories yet use the actual       ┃
+# ┃ locations and code paths.                                                 ┃
+# ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+my $dsh = "$FindBin::Bin/../script/deb-systemd-helper";
+
+sub _unit_check {
+    my ($unit_file, $cmd, $cb, $verb) = @_;
+
+    my $retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh $cmd $unit_file");
+    isnt($retval, -1, 'deb-systemd-helper could be executed');
+    ok(!($retval & 127), 'deb-systemd-helper did not exit due to a signal');
+    $cb->($retval >> 8, 0, "random unit file $unit_file $verb $cmd");
+}
+
+sub is_enabled { _unit_check($_[0], 'is-enabled', \&is, 'is') }
+sub isnt_enabled { _unit_check($_[0], 'is-enabled', \&isnt, 'isnt') }
+
+sub is_debian_installed { _unit_check($_[0], 'debian-installed', \&is, 'is') }
+sub isnt_debian_installed { _unit_check($_[0], 'debian-installed', \&isnt, 'isnt') }
+
+my $retval = Linux::Clone::unshare Linux::Clone::NEWNS;
+BAIL_OUT("Cannot unshare(NEWNS): $!") if $retval != 0;
+
+sub bind_mount_tmp {
+    my ($dir) = @_;
+    my $tmp = tempdir(CLEANUP => 1);
+    system("mount -n --bind $tmp $dir") == 0
+        or BAIL_OUT("bind-mounting $tmp to $dir failed: $!");
+    return $tmp;
+}
+
+my $etc_systemd = bind_mount_tmp('/etc/systemd');
+my $lib_systemd = bind_mount_tmp('/lib/systemd');
+my $var_lib_systemd = bind_mount_tmp('/var/lib/systemd');
+
+# ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+# ┃ Create two unit files with random names; one refers to the other (Also=). ┃
+# ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+my ($fh1, $random_unit1) = tempfile('unitXXXXX',
+    SUFFIX => '.service',
+    TMPDIR => 1,
+    UNLINK => 1);
+close($fh1);
+$random_unit1 = basename($random_unit1);
+
+my ($fh2, $random_unit2) = tempfile('unitXXXXX',
+    SUFFIX => '.service',
+    TMPDIR => 1,
+    UNLINK => 1);
+close($fh2);
+$random_unit2 = basename($random_unit2);
+
+my $servicefile_path1 = "/lib/systemd/system/$random_unit1";
+my $servicefile_path2 = "/lib/systemd/system/$random_unit2";
+make_path('/lib/systemd/system');
+open($fh1, '>', $servicefile_path1);
+print $fh1 <<EOT;
+[Unit]
+Description=test unit
+
+[Service]
+ExecStart=/bin/sleep 1
+
+[Install]
+WantedBy=multi-user.target
+Also=$random_unit2
+EOT
+close($fh1);
+
+open($fh2, '>', $servicefile_path2);
+print $fh2 <<EOT;
+[Unit]
+Description=test unit
+
+[Service]
+ExecStart=/bin/sleep 1
+
+[Install]
+WantedBy=multi-user.target
+Alias=alias2.service
+EOT
+close($fh2);
+
+isnt_enabled($random_unit1);
+isnt_enabled($random_unit2);
+isnt_debian_installed($random_unit1);
+isnt_debian_installed($random_unit2);
+
+# ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+# ┃ Verify “enable” creates all symlinks.                                     ┃
+# ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+ok(! -d '/etc/systemd/system/multi-user.target.wants',
+    'multi-user.target.wants does not exist yet');
+
+$retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh enable $random_unit1");
+my %links = map { (basename($_), readlink($_)) }
+    </etc/systemd/system/multi-user.target.wants/*.service>;
+is_deeply(
+    \%links,
+    {
+        $random_unit1 => $servicefile_path1,
+        $random_unit2 => $servicefile_path2,
+    },
+    'All expected links present');
+
+my $alias_path = '/etc/systemd/system/alias2.service';
+ok(-l $alias_path, 'alias created');
+is(readlink($alias_path), $servicefile_path2,
+    'alias points to the correct service file');
+
+# ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+# ┃ Verify “is-enabled” now returns true.                                     ┃
+# ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+is_enabled($random_unit1);
+is_enabled($random_unit2);
+is_debian_installed($random_unit1);
+
+# $random_unit2 was only enabled _because of_ $random_unit1’s Also= statement
+# and thus does not have its own state file.
+isnt_debian_installed($random_unit2);
+
+# TODO: cleanup tests?
+
+done_testing;