tests: improve testing (#80)

* chore: setup mini.test

* chore(ci): setup new test runner, install plugin deps

* chore(ci): test only on stable and nightly releases

* test: iferr

* test: struct_tags

* test: impl

* test: gotests

spec/integration/iferr_test.lua

@@ -0,0 +1,26 @@
+local t = require "spec.testutils"
+
+local child = MiniTest.new_child_neovim()
+local T = MiniTest.new_set {
+  hooks = {
+    post_once = child.stop,
+    pre_case = function()
+      child.restart { "-u", t.mininit_path }
+    end,
+  },
+}
+T["iferr"] = MiniTest.new_set {}
+T["iferr"]["works"] = function()
+  local tmp = t.tmpfile()
+  local fixtures = t.get_fixtures "iferr/iferr"
+  t.writefile(tmp, fixtures.input)
+
+  child.cmd("silent edit " .. tmp)
+  child.fn.setpos(".", { child.fn.bufnr "%", 8, 2, 0 })
+  child.cmd "GoIfErr"
+  child.cmd "write"
+
+  t.eq(t.readfile(tmp), fixtures.output)
+end
+
+return T