1 files changed, 65 insertions, 0 deletions
diff --git a/test/ruby/test_string_memory.rb b/test/ruby/test_string_memory.rb
new file mode 100644
index 0000000000..a93a3bd54a
--- /dev/null
+++ b/test/ruby/test_string_memory.rb
@@ -0,0 +1,65 @@
+# frozen_string_literal: false
+require 'test/unit'
+require 'objspace'
+
+class TestStringMemory < Test::Unit::TestCase
+  def capture_allocations(klass)
+    allocations = []
+
+    EnvUtil.without_gc do
+      GC.start
+      generation = GC.count
+
+      ObjectSpace.trace_object_allocations do
+        yield
+
+        ObjectSpace.each_object(klass) do |instance|
+          allocations << instance if ObjectSpace.allocation_generation(instance) == generation
+        end
+      end
+
+      return allocations.map do |instance|
+        [
+          ObjectSpace.allocation_sourcefile(instance),
+          ObjectSpace.allocation_sourceline(instance),
+          instance.class,
+          instance,
+        ]
+      end.select do |path,|
+        # drop strings not created in this file
+        # (the parallel testing framework may create strings in a separate thread)
+        path == __FILE__
+      end
+    end
+  end
+
+  def test_byteslice_prefix
+    string = ("a" * 100_000).freeze
+
+    allocations = capture_allocations(String) do
+      string.byteslice(0, 50_000)
+    end
+
+    assert_equal 1, allocations.size, "One object allocation is expected, but allocated: #{ allocations.inspect }"
+  end
+
+  def test_byteslice_postfix
+    string = ("a" * 100_000).freeze
+
+    allocations = capture_allocations(String) do
+      string.byteslice(50_000, 100_000)
+    end
+
+    assert_equal 1, allocations.size, "One object allocation is expected, but allocated: #{ allocations.inspect }"
+  end
+
+  def test_byteslice_postfix_twice
+    string = ("a" * 100_000).freeze
+
+    allocations = capture_allocations(String) do
+      string.byteslice(50_000, 100_000).byteslice(25_000, 50_000)
+    end
+
+    assert_equal 2, allocations.size, "Two object allocations are expected, but allocated: #{ allocations.inspect }"
+  end
+end