test: add for utils

* Add tests only for gopher._utils.empty()

spec/gopher_utils_spec.lua

@@ -0,0 +1,19 @@
+describe("gopher._utils", function()
+  it("can be requried", function()
+    require "gopher._utils"
+  end)
+
+  it(".empty() with non-empty talbe", function()
+    local empty = require("gopher._utils").empty
+    local res = empty { first = "1", second = 2 }
+
+    assert.are.same(res, false)
+  end)
+
+  it(".empty() with empty talbe", function()
+    local empty = require("gopher._utils").empty
+    local res = empty {}
+
+    assert.are.same(res, true)
+  end)
+end)