diff --git a/tool/lib/test/unit/assertions.rb b/tool/lib/test/unit/assertions.rb
index 14442c0029..2dfc09cfb4 100644
--- a/tool/lib/test/unit/assertions.rb
+++ b/tool/lib/test/unit/assertions.rb
@@ -215,16 +215,6 @@ EOT
       alias assert_include assert_includes
       alias assert_not_include assert_not_includes
 
-      def assert_all?(obj, m = nil, &blk)
-        failed = []
-        obj.each do |*a, &b|
-          unless blk.call(*a, &b)
-            failed << (a.size > 1 ? a : a[0])
-          end
-        end
-        assert(failed.empty?, message(m) {failed.pretty_inspect})
-      end
-
       def assert_not_all?(obj, m = nil, &blk)
         failed = []
         obj.each do |*a, &b|
diff --git a/tool/lib/test/unit/core_assertions.rb b/tool/lib/test/unit/core_assertions.rb
index ff78c2bdfa..63478d70b2 100644
--- a/tool/lib/test/unit/core_assertions.rb
+++ b/tool/lib/test/unit/core_assertions.rb
@@ -718,6 +718,16 @@ eom
         end
       end
 
+      def assert_all?(obj, m = nil, &blk)
+        failed = []
+        obj.each do |*a, &b|
+          unless blk.call(*a, &b)
+            failed << (a.size > 1 ? a : a[0])
+          end
+        end
+        assert(failed.empty?, message(m) {failed.pretty_inspect})
+      end
+
       def assert_all_assertions(msg = nil)
         all = AllFailures.new
         yield all