fix: bedrock exception could be found at end of a stream (#2654)

lua/avante/utils/test.lua

@@ -0,0 +1,15 @@
+-- This is a helper for unit tests.
+local M = {}
+
+function M.read_file(fn)
+  fn = vim.uv.cwd() .. "/" .. fn
+  local file = io.open(fn, "r")
+  if file then
+    local data = file:read("*all")
+    file:close()
+    return data
+  end
+  return fn
+end
+
+return M