test: add test for config

spec/unit/config_test.lua

@@ -0,0 +1,22 @@
+local t = require "spec.testutils"
+local _, T = t.setup "config"
+
+T["config"]["can be called without any arguments passed"] = function()
+  ---@diagnostic disable-next-line: missing-parameter
+  require("gopher").setup()
+end
+
+T["config"]["can be called with empty table"] = function()
+  require("gopher").setup {}
+end
+
+T["config"]["should change option"] = function()
+  local log_level = 1234567890
+  require("gopher").setup {
+    log_level = log_level,
+  }
+
+  t.eq(log_level, require("gopher.config").log_level)
+end
+
+return T