This lets us run non-fish targets (such as `fish_tests`) under a clean
test environment without running into the fish-specific payload
configuration now carried out by `test_driver.sh` which expects a
`.fish` payload that it will run under a deterministically configured
instance of fish, running in an environment initialized by
`test_env.sh`.
This should fix the problem with in-tree builds leaving detritus behind
after a `make test` when `fish_tests` would be executed without
`test_driver.sh` - it is now executed under `test_env.sh` instead.
Tests are now executed in a test-specific temporary directory, so test
output on failure should be reproducible/reusable as-is without needing
to have TMPDIR defined (as it only exists by default under macOS).
Aside from the fact that the shared state could cause problems, tests
were randomly assuming it would be created where that wasn't the case.
In particular, `redirect.fish` and `basic.fish` were failing on only
macOS because `../test/temp` didn't exist yet - it would be created by
other tests later.
Even though we are using CMake's ctest for testing, we still define our
own `make test` target rather than use its default for many reasons:
* CMake doesn't run tests in-proc or even add each tests as an
individual node in the ninja dependency tree, instead it just bundles
all tests into a target called `test` that always just shells out to
`ctest`, so there are no build-related benefits to not doing that
ourselves.
* CMake devs insist that it is appropriate for `make test` to never
depend on `make all`, i.e. running `make test` does not require any
of the binaries to be built before testing.
* The only way to have a test depend on a binary is to add a fake test
with a name like "build_fish" that executes CMake recursively to
build the `fish` target.
* It is not possible to set top-level CTest options/settings such as
CTEST_PARALLEL_LEVEL from within the CMake configuration file.
* Circling back to the point about individual tests not being actual
Makefile targets, CMake does not offer any way to execute a named
test via the `make`/`ninja`/whatever interface; the only way to
manually invoke test `foo` is to to manually run `ctest` and specify
a regex matching `foo` as an argument, e.g. `ctest -R ^foo$`... which
is really crazy.
With this patch, it is now possible to execute any single test by name,
by invoking the build directly, e.g. to run the `universal.fish` check:
`cmake --build build --target universal.fish` or
`ninja -C build universal.fish`. Unfortunately, this is not integrated
into the Makefile wrapper, so `make universal.fish` won't work (although
this can potentially be hacked around).
