Default GROUP to "All" which runs Core tests for now

Running Pkg.test() without setting GROUP now uses "All", which currently
maps to Core tests. This can be expanded later to include more groups.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: claude

test/runtests.jl

@@ -1,15 +1,15 @@
 using Pkg
 using Test
 
-const GROUP = get(ENV, "GROUP", "Core")
+const GROUP = get(ENV, "GROUP", "All")
 
 function activate_env(env_dir)
     Pkg.activate(env_dir)
     Pkg.develop(PackageSpec(path = dirname(@__DIR__)))
     return Pkg.instantiate()
 end
 
-if GROUP == "Core"
+if GROUP == "All" || GROUP == "Core"
     @time @testset "Core" begin
         include("core_tests.jl")
     end
@@ -42,5 +42,5 @@ elseif GROUP == "nopre"
         include("nopre/aqua_tests.jl")
     end
 else
-    error("Unknown test group: $GROUP")
+    error("Unknown test group: $GROUP. Valid groups: All, Core, Autodiff, GPU, Downstream, Reactant, nopre")
 end