Reorder tests to not use the same number (#2947)

Distinct numbers make re-running individual tests easier by helping with
tab-completion.

Completeness verified using:
% for i in $(seq 0 600)
do
  files=$(ls testcases/t/$(printf "%03d" $i)-*.t 2>&- | wc -l)
  [ "$files" != "0" ] && [ "$files" != "1" ] && echo "clash: $i"
done

testcases/t/288-i3-floating-window-atom.t

@@ -0,0 +1,70 @@
+#!perl
+# vim:ts=4:sw=4:expandtab
+#
+# Please read the following documents before working on tests:
+# • http://build.i3wm.org/docs/testsuite.html
+#   (or docs/testsuite)
+#
+# • http://build.i3wm.org/docs/lib-i3test.html
+#   (alternatively: perldoc ./testcases/lib/i3test.pm)
+#
+# • http://build.i3wm.org/docs/ipc.html
+#   (or docs/ipc)
+#
+# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+#   (unless you are already familiar with Perl)
+#
+# Tests for our proprietary atom I3_FLOATING_WINDOW to allow
+# identifying floating windows.
+# Ticket: #2223
+use i3test;
+use X11::XCB qw(:all);
+
+my ($con);
+
+sub has_i3_floating_window {
+    sync_with_i3;
+
+    my ($con) = @_;
+    my $cookie = $x->get_property(
+        0,
+        $con->{id},
+        $x->atom(name => 'I3_FLOATING_WINDOW')->id,
+        $x->atom(name => 'CARDINAL')->id,
+        0,
+        1
+    );
+
+    my $reply = $x->get_property_reply($cookie->{sequence});
+    return 0 if $reply->{length} != 1;
+
+    return unpack("L", $reply->{value});
+}
+
+###############################################################################
+# Toggling floating on a container adds / removes I3_FLOATING_WINDOW.
+###############################################################################
+
+fresh_workspace;
+
+$con = open_window;
+is(has_i3_floating_window($con), 0, 'I3_FLOATING_WINDOW is not set');
+
+cmd 'floating enable';
+is(has_i3_floating_window($con), 1, 'I3_FLOATING_WINDOW is set');
+
+cmd 'floating disable';
+is(has_i3_floating_window($con), 0, 'I3_FLOATING_WINDOW is not set');
+
+###############################################################################
+# A window that is floated when managed has I3_FLOATING_WINDOW set.
+###############################################################################
+#
+fresh_workspace;
+
+$con = open_floating_window;
+is(has_i3_floating_window($con), 1, 'I3_FLOATING_WINDOW is set');
+
+###############################################################################
+
+done_testing;