Try deferred Garbage collection.

spec/spec_helper.rb

@@ -123,4 +123,12 @@
   # test failures related to randomization by passing the same `--seed` value
   # as the one that triggered the failure.
   Kernel.srand config.seed
+
+  config.before(:all) do
+    DeferredGarbageCollection.start
+  end
+
+  config.after(:all) do
+    DeferredGarbageCollection.reconsider
+  end
 end

spec/support/deferred_garbage_collection.rb

@@ -0,0 +1,18 @@
+class DeferredGarbageCollection
+  DEFERRED_GC_THRESHOLD = (ENV['DEFER_GC'] || 10.0).to_f
+
+  @@last_gc_run = Time.current
+
+  def self.start
+    GC.disable if DEFERRED_GC_THRESHOLD > 0
+  end
+
+  def self.reconsider
+    if DEFERRED_GC_THRESHOLD > 0 && Time.current - @@last_gc_run >= DEFERRED_GC_THRESHOLD
+      GC.enable
+      GC.start
+      GC.disable
+      @@last_gc_run = Time.current
+    end
+  end
+end