fix: Abort testing if treesitter not available

Author: Andrew Ferrier

tests/debugprint.lua

@@ -1,3 +1,14 @@
+local function requiref(module)
+    require(module)
+end
+
+local ts_utils_test = pcall(requiref, "nvim-treesitter.ts_utils")
+
+if not ts_utils_test then
+    print("Treesitter is not installed; aborting testing.")
+    os.exit(1)
+end
+
 local set_lines = function(lines)
     vim.api.nvim_buf_set_lines(0, 0, -1, false, lines)
 end