'llvm-triple' => 'tesla get-triple'.

Run the "figure out what my LLVM triple is" tool in the same way as all of the other tools.
Improve error message.

If TESLA_BUILD_DIR isn't set [correctly], just say so rather than relying on mysterious PATH error messages.
tesla-test needn't depend on libtesla-test.

If you want to run all tests, just exercise the 'test' target. Otherwise, allow libtesla and the tesla tools to be tested separately.
Oops: add (missing) tesla-cat to 'tesla' usage.
Rewrite 'tesla' script.

Rather than using an ever-growing list of directories to add to $PATH, just use 'find' to look for the desired TESLA tool explicitly under TESLA_BUILD_DIR.

This should be much clearer and require less maintenance (although the usage string will still need manual updating).