feat(test): add tests for throttle function

spec/utils/async_spec.lua

@@ -0,0 +1,47 @@
+---@diagnostic disable: need-check-nil
+local async = require("neocomplete.utils.async")
+
+describe("Throttle", function()
+    local count
+    before_each(function()
+        count = 0
+    end)
+    local test_func = function()
+        count = count + 1
+    end
+    it("makes first call immediately", function()
+        local start = vim.uv.now()
+        local fn = async.throttle(test_func, 100)
+        fn()
+        vim.wait(1000, function()
+            return count == 1
+        end)
+        local ms_passed = vim.uv.now() - start
+        assert.is.truthy(ms_passed < 30)
+    end)
+
+    it("waits for timeout before second call", function()
+        local start = vim.uv.now()
+        local fn = async.throttle(test_func, 100)
+        fn()
+        fn()
+        vim.wait(1000, function()
+            return count == 2
+        end)
+        local ms_passed = vim.uv.now() - start
+        assert.is.truthy(ms_passed > 100 and ms_passed < 200)
+    end)
+
+    it("doesn't queue up more than one call", function()
+        local start = vim.uv.now()
+        local fn = async.throttle(test_func, 100)
+        fn()
+        fn()
+        fn()
+        vim.wait(1000, function()
+            return count == 3
+        end)
+        local ms_passed = vim.uv.now() - start
+        assert.is.truthy(ms_passed > 1000)
+    end)
+end)