Avoid reinstalling parser in tests

Uses a custom function in the faker user config.  This function can be
called via RPC in the process under test.

.gitignore

@@ -1,6 +1,7 @@
 # Tag file created by Vim
 doc/tags
-test/xdg/config/nvim/
+
+# Fake user directory structures
 test/xdg/local/share/nvim/
 test/xdg/local/state/nvim/
 !test/xdg/local/share/nvim/site/pack/testing/start/rainbow-delimiters

test/e2e/config.lua

@@ -71,7 +71,7 @@ describe('User settings are respected', function()
 			end)
 
 			it('Uses the strategy returned by the thunk', function()
-				request('nvim_command', 'TSInstallSync! lua')
+				request(exec_lua, 'TSEnsure(...)', {'lua'})
 				request(buf_set_lines, 0, 0, -1, true, {'print "Hello world"', '-- vim:ft=lua'})
 				request('nvim_command', 'filetype detect')
 				local attachments = request(exec_lua, 'return the_strategy.attachments[1]', {})
@@ -79,7 +79,7 @@ describe('User settings are respected', function()
 			end)
 
 			it('Does nothing if the thunk returns nil', function()
-				request('nvim_command', 'TSInstallSync! vim')
+				request(exec_lua, 'TSEnsure(...)', {'vim'})
 				request(buf_set_lines, 0, 0, -1, true, {'echo "Hello world"', '" vim:ft=vim'})
 				request('nvim_command', 'filetype detect')
 				local attachments = request(exec_lua, 'return the_strategy.attachments[1]', {})

test/xdg/config/nvim/plugin/ts-ensure.lua

@@ -0,0 +1,14 @@
+local get_runtime_file = vim.api.nvim_get_runtime_file
+local parser_pattern = 'parser/%s.*'
+
+---Wrapper around the `:TSinstall` command which will only install a parser if
+---it is not installed yet
+---@param lang string  Language to install
+function TSEnsure(lang, ...)
+	for _, l in ipairs({lang, ...}) do
+		local parsers = get_runtime_file(parser_pattern:format(l), true)
+		if #parsers == 0 then
+			vim.cmd {cmd = 'TSInstallSync', args = {l}}
+		end
+	end
+end