meson test only builds what's required to run a test. If you start with a clean build directory (or run ninja clean), then about half the tests fail because the required plugins or even the loaders themselves have not yet been built.
This adds the proper dependencies so that all requirements are built before testing.
The name of the macro used to pass through the build directory has also been made consistent, so that it could be automatically generated.

ninja clean and then meson test, and all tests now pass.

Also ninja clean and meson test "test name" for all test names, and each individual test passes.