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/gotests_test.lua

@@ -0,0 +1,47 @@
+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["gotests"] = MiniTest.new_set {}
+
+--- NOTE: :GoTestAdd is the only place that has actual logic
+--- All other parts are handled `gotests` itself.
+
+---@param fpath string
+---@return string
+local function read_testfile(fpath)
+  return t.readfile(fpath:gsub(".go", "_test.go"))
+end
+
+T["gotests"]["should add test for function under cursor"] = function()
+  local tmp = t.tmpfile()
+  local fixtures = t.get_fixtures "tests/function"
+  t.writefile(tmp, fixtures.input)
+
+  child.cmd("silent edit " .. tmp)
+  child.fn.setpos(".", { child.fn.bufnr "%", 3, 6 })
+  child.cmd "GoTestAdd"
+
+  t.eq(fixtures.output, read_testfile(tmp))
+end
+
+T["gotests"]["should add test for method under cursor"] = function()
+  local tmp = t.tmpfile()
+  local fixtures = t.get_fixtures "tests/method"
+  t.writefile(tmp, fixtures.input)
+
+  child.cmd("silent edit " .. tmp)
+  child.fn.setpos(".", { child.fn.bufnr "%", 5, 19 })
+  child.cmd "GoTestAdd"
+
+  t.eq(fixtures.output, read_testfile(tmp))
+end
+
+return T