test/ruby/test_gc_compact.rb: Use assert_separately for debugging

... the following timeout failure.

http://rubyci.s3.amazonaws.com/rhel_zlinux/ruby-master/log/20210408T213303Z.fail.html.gz
```
[ 8871/21204] TestGCCompact#test_ast_compactstimeout: output interval exceeds 600.0 seconds.
timeout: the process group 28416 is alive.
PSOUT  PGID   PID     ELAPSED %CPU    VSZ COMMAND         COMMAND
PSOUT 28416 28416       12:46  0.0 108120 gmake           gmake TESTS=--hide-skip -v RUBYOPT=-w test-all
PSOUT 28416 28423       12:46 88.2 1446124 ruby           ./test/runner.rb: TestGCCompact#test_ast_compacts
timeout: INT signal sent.
timeout: INT signal sent.
timeout: TERM signal sent.
timeout: TERM signal sent.
timeout: KILL signal sent.
```

This error repeatedly occurs on RHEL s390x.

This change sends SEGV when timeout occurs so that it should dump the backtrace.

1 files changed, 13 insertions, 11 deletions

diff --git a/test/ruby/test_gc_compact.rb b/test/ruby/test_gc_compact.rb
index 4a8cff33f4..8dfa66a177 100644
--- a/test/ruby/test_gc_compact.rb
+++ b/test/ruby/test_gc_compact.rb
@@ -133,18 +133,20 @@ class TestGCCompact < Test::Unit::TestCase
     assert_equal hash, list_of_objects.hash
   end
 
-  def walk_ast ast
-    children = ast.children.grep(RubyVM::AbstractSyntaxTree::Node)
-    children.each do |child|
-      assert child.type
-      walk_ast child
-    end
-  end
-
   def test_ast_compacts
-    ast = RubyVM::AbstractSyntaxTree.parse_file __FILE__
-    assert GC.compact
-    walk_ast ast
+    assert_separately([], "#{<<~"begin;"}\n#{<<~"end;"}", timeout: 10, signal: :SEGV)
+    begin;
+      def walk_ast ast
+        children = ast.children.grep(RubyVM::AbstractSyntaxTree::Node)
+        children.each do |child|
+          assert child.type
+          walk_ast child
+        end
+      end
+      ast = RubyVM::AbstractSyntaxTree.parse_file #{__FILE__.dump}
+      assert GC.compact
+      walk_ast ast
+    end;
   end
 
   def test_compact_count