+ Added project file and executable for built-in test

alire.toml

@@ -28,10 +28,11 @@ version = "0.2.0"
 authors = ["Vinzent \"Jellix\" Saranen"]
 website = "https://github.heisenbug.eu/si_units"
 licenses = ["WTFPL"]
+tags = ["utilities", "formatting"]
 maintainers = ["[email protected]"]
 maintainers-logins = ["Jellix"]
-project-files = ["si_units.gpr"]
-tags = ["utilities", "formatting"]
+project-files = ["si_units.gpr", "test/si_units_test.gpr"]
+executables = ["main_si_units_test"]
 
 [gpr-externals]
 SI_UNITS_BUILD_MODE = ["debug", "release"]