fix(picker.config): better config merging and tests

tests/config_spec.lua

@@ -0,0 +1,46 @@
+---@module 'luassert'
+
+local function d(v)
+  return vim.inspect(v):gsub("%s+", " ")
+end
+
+describe("config", function()
+  local tests = {
+    {
+      { 1, 2 },
+      { 3, 4 },
+      { 3, 4 },
+    },
+    {
+      { 1, 2 },
+      nil,
+      { 1, 2 },
+    },
+    {
+      { a = 1, b = 2 },
+      { c = 3 },
+      { a = 1, b = 2, c = 3 },
+    },
+    {
+      { 1, 2, a = 1 },
+      { 3, 4, b = 2 },
+      { 3, 4, b = 2 },
+    },
+    {
+      { 3, 4, b = 2 },
+      { 1, 2 },
+      { 1, 2 },
+    },
+    {
+      { 1, 2, a = 1 },
+      { b = 2 },
+      { 1, 2, b = 2, a = 1 },
+    },
+  }
+  for _, t in ipairs(tests) do
+    it("merges correctly " .. d(t), function()
+      local ret = Snacks.config.merge(t[1], t[2])
+      assert.are.same(ret, t[3])
+    end)
+  end
+end)