diff --git a/zig-ecs/src/ecs/groups.zig b/zig-ecs/src/ecs/groups.zig
index 3cb682b..95c30f7 100644
--- a/zig-ecs/src/ecs/groups.zig
+++ b/zig-ecs/src/ecs/groups.zig
@@ -218,4 +218,4 @@ test "multiple OwningGroups" {
 
     // this will break the group
     // var group6 = reg.group(.{Sprite, Rotation}, .{}, .{});
-}
\ No newline at end of file
+}
diff --git a/zig-ecs/src/ecs/registry.zig b/zig-ecs/src/ecs/registry.zig
index 842d63e..d79cc60 100644
--- a/zig-ecs/src/ecs/registry.zig
+++ b/zig-ecs/src/ecs/registry.zig
@@ -283,6 +283,13 @@ pub const Registry = struct {
         self.add(entity, value);
     }
 
+    /// adds all the component types passed in as zero-initialized values
+    pub fn addTypes(self: *Registry, entity: Entity, comptime types: var) void {
+        inline for (types) |t| {
+            self.assure(t).add(entity, std.mem.zeroes(t));
+        }
+    }
+
     /// Replaces the given component for an entity
     pub fn replace(self: *Registry, entity: Entity, value: var) void {
         assert(self.valid(entity));
@@ -519,7 +526,6 @@ pub const Registry = struct {
                 }
 
                 const check = overlapping == 0 or ((sz == size) or (sz == grp.size));
-                std.debug.warn("overlapping: {}, sz: {}, (sz == size): {}, (sz == gdata.size): {}\t--- check: {}\n", .{ overlapping, sz, sz == size, sz == grp.size, check });
                 std.debug.assert(check);
             }
         }
@@ -571,8 +577,7 @@ pub const Registry = struct {
                 new_group_data.entity_set.add(entity);
             }
         } else {
-            // we cannot iterate backwards because we want to leave behind valid entities in case of owned types
-            // maybeValidIf all the entities in the first owned group
+            // ??we cannot iterate backwards because we want to leave behind valid entities in case of owned types
             var first_owned_storage = self.assure(owned[0]);
             for (first_owned_storage.data().*) |entity| {
                 new_group_data.maybeValidIf(entity);
diff --git a/zig-ecs/tests/groups_test.zig b/zig-ecs/tests/groups_test.zig
new file mode 100644
index 0000000..ced5870
--- /dev/null
+++ b/zig-ecs/tests/groups_test.zig
@@ -0,0 +1,76 @@
+const std = @import("std");
+const warn = std.debug.warn;
+const ecs = @import("ecs");
+const Registry = @import("ecs").Registry;
+
+const Velocity = struct { x: f32 = 0, y: f32 = 0 };
+const Position = struct { x: f32 = 0, y: f32 = 0 };
+const Empty = struct {};
+const Sprite = struct { x: f32 = 0 };
+const Transform = struct { x: f32 = 0 };
+const Renderable = struct { x: f32 = 0 };
+const Rotation = struct { x: f32 = 0 };
+
+fn printStore(store: var, name: []const u8) void {
+    warn("--- {} ---\n", .{name});
+    for (store.set.dense.items) |e, i| {
+        warn("{:3.0}", .{e});
+        warn(" ({d:3.0})", .{store.instances.items[i]});
+    }
+    warn("\n", .{});
+}
+
+test "nested OwningGroups add/remove components" {
+    var reg = Registry.init(std.testing.allocator);
+    defer reg.deinit();
+
+    var group1 = reg.group(.{Sprite}, .{Renderable}, .{});
+    var group2 = reg.group(.{ Sprite, Transform }, .{Renderable}, .{});
+    var group3 = reg.group(.{ Sprite, Transform }, .{ Renderable, Rotation }, .{});
+
+    std.testing.expect(!reg.sortable(Sprite));
+    std.testing.expect(!reg.sortable(Transform));
+    std.testing.expect(reg.sortable(Renderable));
+
+    var e1 = reg.create();
+    reg.addTypes(e1, .{ Sprite, Renderable, Rotation });
+    std.testing.expectEqual(group1.len(), 1);
+    std.testing.expectEqual(group2.len(), 0);
+    std.testing.expectEqual(group3.len(), 0);
+
+    reg.add(e1, Transform{});
+    std.testing.expectEqual(group3.len(), 1);
+
+    reg.remove(Sprite, e1);
+    std.testing.expectEqual(group1.len(), 0);
+    std.testing.expectEqual(group2.len(), 0);
+    std.testing.expectEqual(group3.len(), 0);
+}
+
+test "nested OwningGroups entity order" {
+    var reg = Registry.init(std.testing.allocator);
+    defer reg.deinit();
+
+    var group1 = reg.group(.{Sprite}, .{Renderable}, .{});
+    var group2 = reg.group(.{ Sprite, Transform }, .{Renderable}, .{});
+
+    var i: usize = 0;
+    while (i < 5) : (i += 1) {
+        var e = reg.create();
+        reg.add(e, Sprite{ .x = @intToFloat(f32, i) });
+        reg.add(e, Renderable{ .x = @intToFloat(f32, i) });
+    }
+
+    std.testing.expectEqual(group1.len(), 5);
+    std.testing.expectEqual(group2.len(), 0);
+
+    var sprite_store = reg.assure(Sprite);
+    var transform_store = reg.assure(Transform);
+    printStore(sprite_store, "Sprite");
+
+    reg.add(1, Transform{.x = 1});
+
+    printStore(sprite_store, "Sprite");
+    printStore(transform_store, "Transform");
+    warn("group2.current: {}\n", .{group2.current.*});
+}
diff --git a/zig-ecs/tests/registry_test.zig b/zig-ecs/tests/registry_test.zig
index a730451..b2b7ea8 100644
--- a/zig-ecs/tests/registry_test.zig
+++ b/zig-ecs/tests/registry_test.zig
@@ -3,7 +3,7 @@ const ecs = @import("ecs");
 const Registry = @import("ecs").Registry;
 
 const Velocity = struct { x: f32, y: f32 };
-const Position = struct { x: f32, y: f32 };
+const Position = struct { x: f32 = 0, y: f32 = 0 };
 const Empty = struct {};
 const BigOne = struct { pos: Position, vel: Velocity, accel: Velocity };
 
@@ -17,11 +17,12 @@ test "Registry" {
 
     var e1 = reg.create();
 
-    reg.add(e1, Empty{});
-    reg.add(e1, Position{ .x = 5, .y = 5 });
+    reg.addTypes(e1, .{Empty, Position});
     reg.add(e1, BigOne{ .pos = Position{ .x = 5, .y = 5 }, .vel = Velocity{ .x = 5, .y = 5 }, .accel = Velocity{ .x = 5, .y = 5 } });
 
     std.testing.expect(reg.has(Empty, e1));
+    std.testing.expect(reg.has(Position, e1));
+    std.testing.expect(reg.has(BigOne, e1));
 
     reg.remove(Empty, e1);
     std.testing.expect(!reg.has(Empty, e1));
diff --git a/zig-ecs/tests/tests.zig b/zig-ecs/tests/tests.zig
index 2f11302..10eaf86 100644
--- a/zig-ecs/tests/tests.zig
+++ b/zig-ecs/tests/tests.zig
@@ -1,4 +1,5 @@
 test "ecs test suite" {
     _ = @import("dispatcher_test.zig");
     _ = @import("registry_test.zig");
+    _ = @import("groups_test.zig");
 }