Fix UpdateAsync transform behavior

lib/MockDataStoreService/MockGlobalDataStore.lua

@@ -357,7 +357,21 @@ function MockGlobalDataStore:UpdateAsync(key, transformFunction)
 		error("UpdateAsync rejected with error (request was throttled, but throttled queue was full)", 2)
 	end
 
-	local value = transformFunction(Utils.deepcopy(self.__data[key]))
+	local thread = coroutine.create(function()
+		return transformFunction(Utils.deepcopy(self.__data[key]))
+	end)
+
+	local ok, value = coroutine.resume(thread)
+
+	if coroutine.status(thread) == "suspended" then
+		task.spawn(error, "Transfom function error Callbacks cannot yield")
+		return
+	end
+
+	if not ok then
+		task.spawn(error, `Transform function error {value}`)
+		return
+	end
 
 	if value == nil then -- cancel update after remote call
 		Utils.simulateYield()

spec/MockDataStoreService/MockGlobalDataStore.spec.lua

@@ -693,6 +693,43 @@ return function()
 
         end)
 
+        it("should not throw error to caller when transform function errors", function()
+            Test.reset()
+            Test.setStaticBudgets(100)
+            local MockGlobalDataStore = Test.Service:GetDataStore("Test")
+
+            local ok, value = pcall(function()
+                return MockGlobalDataStore:UpdateAsync("TestKey1", function()
+                    error("intentional error")
+                    return "new value"
+                end)
+            end)
+
+            expect(ok).to.equal(true)
+            expect(value).never.to.be.ok()
+
+        end)
+
+        it("should not succeed when transform function yields", function()
+            Test.reset()
+            Test.setStaticBudgets(100)
+            local MockGlobalDataStore = Test.Service:GetDataStore("Test")
+
+            MockGlobalDataStore:ImportFromJSON({TestKey1 = "value"})
+
+            MockGlobalDataStore:UpdateAsync("TestKey1", function()
+                task.wait()
+                return "new value"
+            end)
+
+            task.wait()
+
+            local exported = HttpService:JSONDecode(MockGlobalDataStore:ExportToJSON())
+
+            expect(exported.TestKey1).to.equal("value")
+
+        end)
+
         it("should consume budgets correctly", function()
             Test.reset()
             Test.setStaticBudgets(100)