diff --git a/crates/lb/tests/task.lua b/crates/lb/tests/task.lua
index 89d7f75..c8693ae 100644
--- a/crates/lb/tests/task.lua
+++ b/crates/lb/tests/task.lua
@@ -3,20 +3,26 @@ if not ok then return end
 
 describe("spawn", function()
   test("callback receives args", function()
-    spawn(function(...)
-      assert(select("#", ...) == 0)
-    end):await()
+    task
+      :spawn(function(...)
+        assert(select("#", ...) == 0)
+      end)
+      :await()
 
-    spawn(function(...)
-      assert(select("#", ...) == 1)
-      assert((...) == nil)
-    end, nil):await()
+    task
+      :spawn(function(...)
+        assert(select("#", ...) == 1)
+        assert((...) == nil)
+      end, nil)
+      :await()
 
-    spawn(function(...)
-      assert(select("#", ...) == 4)
-      local args = table.pack(...)
-      assert(args[1] == 1 and args[2] == 2 and args[3] == nil and args[4] == 3)
-    end, 1, 2, nil, 3):await()
+    task
+      :spawn(function(...)
+        assert(select("#", ...) == 4)
+        local args = table.pack(...)
+        assert(args[1] == 1 and args[2] == 2 and args[3] == nil and args[4] == 3)
+      end, 1, 2, nil, 3)
+      :await()
   end)
 
   test("await returns callback results", function()
@@ -54,3 +60,15 @@ describe("spawn", function()
     assert(res.n == 3 and res[1] == 1 and res[2] == 3 and res[3] == nil)
   end)
 end)
+
+describe("sleep", function()
+  test("sleep is asynchronous", function()
+    local value
+    spawn(function()
+      value = "value"
+    end)
+    assert(value == nil)
+    sleep(100) -- implicit await: if it's synchronous, value wouldn't change
+    assert(value == "value")
+  end)
+end)