diff --git a/testcases/lib/i3test.pm b/testcases/lib/i3test.pm
index 86886de1..fe3b50c6 100644
--- a/testcases/lib/i3test.pm
+++ b/testcases/lib/i3test.pm
@@ -34,7 +34,6 @@ our @EXPORT = qw(
     get_dock_clients
     cmd
     sync_with_i3
-    does_i3_live
     exit_gracefully
     workspace_exists
     focused_ws
@@ -459,13 +458,6 @@ sub sync_with_i3 {
     };
 }
 
-sub does_i3_live {
-    my $tree = i3(get_socket_path())->get_tree->recv;
-    my @nodes = @{$tree->{nodes}};
-    my $ok = (@nodes > 0);
-    $tester->ok($ok, 'i3 still lives');
-    return $ok;
-}
 
 # Tries to exit i3 gracefully (with the 'exit' cmd) or kills the PID if that fails
 sub exit_gracefully {
diff --git a/testcases/lib/i3test/Test.pm b/testcases/lib/i3test/Test.pm
index 4389971b..0253bc2d 100644
--- a/testcases/lib/i3test/Test.pm
+++ b/testcases/lib/i3test/Test.pm
@@ -6,6 +6,7 @@ use base 'Test::Builder::Module';
 our @EXPORT = qw(
     is_num_children
     cmp_float
+    does_i3_live
 );
 
 my $CLASS = __PACKAGE__;
@@ -83,6 +84,22 @@ sub cmp_float {
   $tb->cmp_ok(abs($a - $b), '<', 1e-6, $name);
 }
 
+=head2 does_i3_live
+
+Returns true if the layout tree can still be received from i3.
+
+  # i3 used to crash on invalid commands in revision X
+  cmd 'invalid command';
+  does_i3_live;
+
+=cut
+sub does_i3_live {
+    my $tree = i3test::i3(i3test::get_socket_path())->get_tree->recv;
+    my @nodes = @{$tree->{nodes}};
+    my $tb = $CLASS->builder;
+    $tb->ok((@nodes > 0), 'i3 still lives');
+}
+
 =head1 AUTHOR
 
 Michael Stapelberg <michael@i3wm.org>