Add spec

spec/feature/array_size_spec.rb

@@ -0,0 +1,12 @@
+describe 'Array size' do
+  let(:input) do
+    # default array size max is 131072
+    # src/array.c:21: #define MRB_ARY_LENGTH_MAX 131072
+    140_000.times.to_a.join("\n")
+  end
+
+  let(:args) { '-s _.size' }
+  let(:expect_output) { '140000' }
+
+  it_behaves_like 'a successful exec'
+end