Initial sketch of automated indent tests

lua/nvim-treesitter/test_utils.lua

@@ -0,0 +1,25 @@
+local M = {}
+
+function M.indent_whole_file(file)
+  assert.are.same(1, vim.fn.filereadable(file))
+
+  -- load reference file
+  vim.cmd(string.format('edit %s', file))
+  local reference = vim.api.nvim_buf_get_lines(0, 0, -1, true)
+
+  -- FIXME: why this is not set automatically?
+  vim.bo.indentexpr = 'nvim_treesitter#indent()'
+  assert.are.same('nvim_treesitter#indent()', vim.bo.indentexpr)
+
+  -- indent the whole file
+  vim.cmd 'normal gg=G'
+  local indented =  vim.api.nvim_buf_get_lines(0, 0, -1, true)
+
+  -- clear any changes to avoid 'No write since last change (add ! to override)'
+  vim.cmd 'edit!'
+
+  -- compare before and after
+  assert.are.same(reference, indented)
+end
+
+return M