1 files changed, 25 insertions, 0 deletions
diff --git a/spec/ruby/core/string/uminus_spec.rb b/spec/ruby/core/string/uminus_spec.rb
index 53e73b7e67..f18e6b1234 100644
--- a/spec/ruby/core/string/uminus_spec.rb
+++ b/spec/ruby/core/string/uminus_spec.rb
@@ -17,5 +17,30 @@ ruby_version_is "2.3" do
       output.frozen?.should == true
       output.should == 'foo'
     end
+
+    ruby_version_is "2.5" do
+      it "returns the same object for equal unfrozen strings" do
+        origin = "this is a string"
+        dynamic = %w(this is a string).join(' ')
+
+        origin.should_not equal(dynamic)
+        (-origin).should equal(-dynamic)
+      end
+
+      it "returns the same object when it's called on the same String literal" do
+        (-"unfrozen string").should equal(-"unfrozen string")
+        (-"unfrozen string").should_not equal(-"another unfrozen string")
+      end
+
+      it "is an identity function if the string is frozen" do
+        dynamic = %w(this string is frozen).join(' ').freeze
+
+        (-dynamic).should equal(dynamic)
+
+        dynamic.should_not equal("this string is frozen".freeze)
+        (-dynamic).should_not equal("this string is frozen".freeze)
+        (-dynamic).should_not equal(-"this string is frozen".freeze)
+      end
+    end
   end
 end