1 files changed, 60 insertions, 0 deletions
diff --git a/spec/ruby/core/string/uplus_spec.rb b/spec/ruby/core/string/uplus_spec.rb
new file mode 100644
index 0000000000..20767bcc01
--- /dev/null
+++ b/spec/ruby/core/string/uplus_spec.rb
@@ -0,0 +1,60 @@
+# frozen_string_literal: false
+require_relative '../../spec_helper'
+
+describe 'String#+@' do
+  it 'returns an unfrozen copy of a frozen String' do
+    input  = 'foo'.freeze
+    output = +input
+
+    output.should_not.frozen?
+    output.should == 'foo'
+
+    output << 'bar'
+    output.should == 'foobar'
+  end
+
+  it 'returns a mutable String itself' do
+    input = String.new("foo")
+    output = +input
+
+    output.should.equal?(input)
+
+    input << "bar"
+    output.should == "foobar"
+  end
+
+  context 'if file has "frozen_string_literal: true" magic comment' do
+    it 'returns mutable copy of a literal' do
+      ruby_exe(fixture(__FILE__, "freeze_magic_comment.rb")).should == 'mutable'
+    end
+  end
+
+  context 'if file has "frozen_string_literal: false" magic comment' do
+    it 'returns literal string itself' do
+      input  = 'foo'
+      output = +input
+
+      output.equal?(input).should == true
+    end
+  end
+
+  context 'if file has no frozen_string_literal magic comment' do
+    ruby_version_is ''...'3.4' do
+      it 'returns literal string itself' do
+        eval(<<~RUBY).should == true
+          s = "foo"
+          s.equal?(+s)
+        RUBY
+      end
+    end
+
+    ruby_version_is '3.4' do
+      it 'returns mutable copy of a literal' do
+        eval(<<~RUBY).should == false
+          s = "foo"
+          s.equal?(+s)
+        RUBY
+      end
+    end
+  end
+end