Are there any tools to generate VHDL test benches automatically?

The basic answer is no. Writing a testbench can be a complex task, and can be more complex than the design being tested. If you mean "Can I get a code framework for a simple testbench", then a number of tools provide simple "testbench templates"; even the Emacs editor VHDL mode can do this! For more advanced ways of writing testbenches, you might want to look at the so-called "Testbench Automation" tools, such as SystemVerilog, SystemC Verification Library, Cadence Specman, and Synopys Vera. These tools involve learning another language of course. If you want to know how to write more complex testbenches (for instance to cope with data arriving in a different order from the order it entered a device).