diff --git a/testcases/complete-run.pl b/testcases/complete-run.pl
index e28bc19e..083e1ebb 100755
--- a/testcases/complete-run.pl
+++ b/testcases/complete-run.pl
@@ -1,19 +1,38 @@
 #!/usr/bin/env perl
 # vim:ts=4:sw=4:expandtab
+#
+# © 2010-2011 Michael Stapelberg and contributors
+#
+# syntax: ./complete-run.pl --display :1 --display :2
+# to run the test suite on the X11 displays :1 and :2
+# use 'Xdummy :1' and 'Xdummy :2' before to start two
+# headless X11 servers
+#
 
 use strict;
 use warnings;
+use EV;
+use AnyEvent;
+use IO::Scalar; # not in core :\
+use File::Temp qw(tempfile tempdir);
 use v5.10;
 use DateTime;
 use Data::Dumper;
 use Cwd qw(abs_path);
 use Proc::Background;
 use TAP::Harness;
+use TAP::Parser;
 use TAP::Parser::Aggregator;
 use File::Basename qw(basename);
 use AnyEvent::I3 qw(:all);
 use Try::Tiny;
 use Getopt::Long;
+use Time::HiRes qw(sleep);
+
+# install a dummy CHLD handler to overwrite the CHLD handler of AnyEvent / EV
+# XXX: we could maybe also use a different loop than the default loop in EV?
+$SIG{CHLD} = sub {
+};
 
 # reads in a whole file
 sub slurp {
@@ -23,12 +42,20 @@ sub slurp {
 }
 
 my $coverage_testing = 0;
+my @displays = ();
 
 my $result = GetOptions(
-    "coverage-testing" => \$coverage_testing
+    "coverage-testing" => \$coverage_testing,
+    "display=s" => \@displays,
 );
 
-my $i3cmd = "export DISPLAY=:0; exec " . abs_path("../i3") . " -V -d all --disable-signalhandler -c i3-test.config";
+@displays = split(/,/, join(',', @displays));
+@displays = map { s/ //g; $_ } @displays;
+
+@displays = qw(:1) if @displays == 0;
+
+my $i3cmd = abs_path("../i3") . " -V -d all --disable-signalhandler";
+my $config = slurp('i3-test.config');
 
 # 1: get a list of all testcases
 my @testfiles = @ARGV;
@@ -46,40 +73,121 @@ unlink("latest") if -e "latest";
 symlink("$outdir", "latest") or die "Could not symlink latest to $outdir";
 
 # 3: run all tests
-my $harness = TAP::Harness->new({
-    verbosity => 1,
-    lib => [ 't/lib' ]
-});
+my @done;
+my $num = @testfiles;
+my $harness = TAP::Harness->new({ });
+
 my $aggregator = TAP::Parser::Aggregator->new();
 $aggregator->start();
-for my $t (@testfiles) {
-    my $logpath = "$outdir/i3-log-for-" . basename($t);
-    my $cmd = "$i3cmd >$logpath 2>&1";
-    my $dont_start = (slurp($t) =~ /# !NO_I3_INSTANCE!/);
+
+my $cv = AnyEvent->condvar;
+
+# We start tests concurrently: For each display, one test gets started. Every
+# test starts another test after completing.
+take_job($_) for @displays;
+
+#
+# Takes a test from the beginning of @testfiles and runs it.
+#
+# The TAP::Parser (which reads the test output) will get called as soon as
+# there is some activity on the stdout file descriptor of the test process
+# (using an AnyEvent->io watcher).
+#
+# When a test completes and @done contains $num entries, the $cv condvar gets
+# triggered to finish testing.
+#
+sub take_job {
+    my ($display) = @_;
+    my ($fh, $tmpfile) = tempfile();
+    say $fh $config;
+    say $fh "ipc-socket /tmp/nested-$display";
+    close($fh);
+
+    my $test = shift @testfiles;
+    return unless $test;
+    my $logpath = "$outdir/i3-log-for-" . basename($test);
+    my $cmd = "export DISPLAY=$display; exec $i3cmd -c $tmpfile >$logpath 2>&1";
+    my $dont_start = (slurp($test) =~ /# !NO_I3_INSTANCE!/);
 
     my $process = Proc::Background->new($cmd) unless $dont_start;
-    say "testing $t with logfile $logpath";
-    $harness->aggregate_tests($aggregator, [ $t ]);
+    say "[$display] Running $test with logfile $logpath";
 
-    # Don’t bother killing i3 when we haven’t started it
-    next if $dont_start;
+    sleep 0.5;
+    my $kill_i3 = sub {
+        # Don’t bother killing i3 when we haven’t started it
+        return if $dont_start;
 
-    # When measuring code coverage, try to exit i3 cleanly (otherwise, .gcda
-    # files are not written) and fallback to killing it
-    if ($coverage_testing) {
-        my $exited = 0;
-        try {
-            say "Exiting i3 cleanly...";
-            i3("/tmp/nestedcons")->command('exit')->recv;
-            $exited = 1;
-        };
-        next if $exited;
+        # When measuring code coverage, try to exit i3 cleanly (otherwise, .gcda
+        # files are not written) and fallback to killing it
+        if ($coverage_testing) {
+            my $exited = 0;
+            try {
+                say "Exiting i3 cleanly...";
+                i3("/tmp/nested-$display")->command('exit')->recv;
+                $exited = 1;
+            };
+            return if $exited;
+        }
+
+        say "[$display] killing i3";
+        kill(9, $process->pid) or die "could not kill i3";
+    };
+
+    my $output;
+    my $parser = TAP::Parser->new({
+        exec => [ 'sh', '-c', "DISPLAY=$display /usr/bin/perl -It/lib $test" ],
+        spool => IO::Scalar->new(\$output),
+        merge => 1,
+    });
+
+    my @watchers;
+    my ($stdout, $stderr) = $parser->get_select_handles;
+    for my $handle ($parser->get_select_handles) {
+        my $w;
+        $w = AnyEvent->io(
+            fh => $handle,
+            poll => 'r',
+            cb => sub {
+                # Ignore activity on stderr (unnecessary with merge => 1,
+                # but let’s keep it in here if we want to use merge => 0
+                # for some reason in the future).
+                return if defined($stderr) and $handle == $stderr;
+
+                my $result = $parser->next;
+                if (defined($result)) {
+                    # TODO: check if we should bail out
+                    return;
+                }
+
+                # $result is not defined, we are done parsing
+                say "[$display] $test finished";
+                close($parser->delete_spool);
+                $aggregator->add($test, $parser);
+                push @done, [ $test, $output ];
+
+                $kill_i3->();
+
+                undef $_ for @watchers;
+                if (@done == $num) {
+                    $cv->send;
+                } else {
+                    take_job($display);
+                }
+            }
+        );
+        push @watchers, $w;
     }
-
-    say "Killing i3";
-    kill(9, $process->pid) or die "could not kill i3";
 }
+
+$cv->recv;
+
 $aggregator->stop();
 
+for (@done) {
+    my ($test, $output) = @$_;
+    say "output for $test:";
+    say $output;
+}
+
 # 4: print summary
 $harness->summary($aggregator);