Re: [PATCH v2 4/4] t/Makefile: introduce TEST_SHELL_PATH

> You may want to run the test suite with a different shell
> than you use to build Git. For instance, you may build with
> SHELL_PATH=/bin/sh (because it's faster, or it's what you
> expect to exist on systems where the build will be used) but
> want to run the test suite with bash (e.g., since that
> allows using "-x" reliably across the whole test suite).
> There's currently no good way to do this.
> 
> You might think that doing two separate make invocations,
> like:
> 
>   make &&
>   make -C t SHELL_PATH=/bin/bash
> 
> would work. And it _almost_ does. The second make will see
> our bash SHELL_PATH, and we'll use that to run the
> individual test scripts (or tell prove to use it to do so).
> So far so good.
> 
> But this breaks down when "--tee" or "--verbose-log" is
> used. Those options cause the test script to actually
> re-exec itself using $SHELL_PATH. But wait, wouldn't our
> second make invocation have set SHELL_PATH correctly in the
> environment?
> 
> Yes, but test-lib.sh sources GIT-BUILD-OPTIONS, which we
> built during the first "make". And that overrides the
> environment, giving us the original SHELL_PATH again.