test: add rudimentary smoke tests to check for errors

lua/github-theme/_test/util.lua

@@ -0,0 +1,21 @@
+local M = {}
+local api = vim.api
+
+function M.await_VimEnter()
+  if vim.v.vim_did_enter == 0 then
+    local co = assert(coroutine.running(), 'test is not running in coroutine')
+
+    api.nvim_create_autocmd('VimEnter', {
+      pattern = '*',
+      once = true,
+      nested = true,
+      callback = vim.schedule_wrap(function()
+        coroutine.resume(co)
+      end),
+    })
+
+    coroutine.yield()
+  end
+end
+
+return M

test/github-theme/smoketest/startup_spec.lua

@@ -0,0 +1,33 @@
+local assert = require('luassert')
+local t_util = require('github-theme._test.util')
+
+describe('(smoke test)', function()
+  describe('setting colorscheme during startup', function()
+    it('should not error', function()
+      assert.does_not_error(function()
+        vim.cmd('colorscheme github_dark_dimmed')
+      end)
+
+      assert.is.equal('', vim.v.errmsg or '')
+    end)
+  end)
+
+  describe('setting/switching colorscheme post-startup', function()
+    it('should not error', function()
+      t_util.await_VimEnter()
+
+      for _, cs in ipairs({
+        'default',
+        'github_dark_dimmed',
+        'github_dark_dimmed',
+        'github_light',
+      }) do
+        assert.does_not_error(function()
+          vim.cmd('colorscheme ' .. cs)
+        end)
+
+        assert.is.equal('', vim.v.errmsg or '')
+      end
+    end)
+  end)
+end)