1 files changed, 53 insertions, 0 deletions
diff --git a/spec/ruby/core/string/uminus_spec.rb b/spec/ruby/core/string/uminus_spec.rb
new file mode 100644
index 0000000000..43abf71d50
--- /dev/null
+++ b/spec/ruby/core/string/uminus_spec.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: false
+require_relative '../../spec_helper'
+
+describe 'String#-@' do
+  it 'returns self if the String is frozen' do
+    input  = 'foo'.freeze
+    output = -input
+
+    output.should.equal?(input)
+    output.should.frozen?
+  end
+
+  it 'returns a frozen copy if the String is not frozen' do
+    input  = 'foo'
+    output = -input
+
+    output.should.frozen?
+    output.should_not.equal?(input)
+    output.should == 'foo'
+  end
+
+  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 "deduplicates frozen strings" do
+    dynamic = %w(this string is frozen).join(' ').freeze
+
+    dynamic.should_not.equal?("this string is frozen".freeze)
+
+    (-dynamic).should.equal?("this string is frozen".freeze)
+    (-dynamic).should.equal?((-"this string is frozen").freeze)
+  end
+
+  it "does not deduplicate a frozen string when it has instance variables" do
+    dynamic = %w(this string is frozen).join(' ')
+    dynamic.instance_variable_set(:@a, 1)
+    dynamic.freeze
+
+    (-dynamic).should_not.equal?("this string is frozen".freeze)
+    (-dynamic).should_not.equal?((-"this string is frozen").freeze)
+    (-dynamic).should.equal?(-dynamic)
+  end
+end