Improve Module#to_s specs

* Ensure there is no extra output before or after.
  For example, TruffleRuby had an extra leading `#<Class:`.

Author: eregon

spec/ruby/core/class/to_s_spec.rb

@@ -6,6 +6,9 @@ def self.without_test_modules(modules)
 
   CONST = :plain_constant
 
+  class NamedClass
+  end
+
   module PrivConstModule
     PRIVATE_CONSTANT = 1
     private_constant :PRIVATE_CONSTANT

spec/ruby/core/module/fixtures/classes.rb

@@ -2,17 +2,44 @@
 require_relative 'fixtures/classes'
 
 describe "Module#to_s" do
+  it 'returns the name of the module if it has a name' do
+    Enumerable.to_s.should == 'Enumerable'
+    String.to_s.should == 'String'
+  end
+
   it "returns the full constant path leading to the module" do
     ModuleSpecs::LookupMod.to_s.should == "ModuleSpecs::LookupMod"
   end
 
   it "works with an anonymous module" do
     m = Module.new
-    m.to_s.should =~ /#<Module:0x[0-9a-f]+>/
+    m.to_s.should =~ /\A#<Module:0x\h+>\z/
   end
 
   it "works with an anonymous class" do
     c = Class.new
-    c.to_s.should =~ /#<Class:0x[0-9a-f]+>/
+    c.to_s.should =~ /\A#<Class:0x\h+>\z/
+  end
+
+  it 'for the singleton class of an object of an anonymous class' do
+    klass = Class.new
+    obj = klass.new
+    sclass = obj.singleton_class
+    sclass.to_s.should == "#<Class:#{obj}>"
+    sclass.to_s.should =~ /\A#<Class:#<#{klass}:0x\h+>>\z/
+    sclass.to_s.should =~ /\A#<Class:#<#<Class:0x\h+>:0x\h+>>\z/
+  end
+
+  it 'for a singleton class of a module includes the module name' do
+    ModuleSpecs.singleton_class.to_s.should == '#<Class:ModuleSpecs>'
+  end
+
+  it 'for a metaclass includes the class name' do
+    ModuleSpecs::NamedClass.singleton_class.to_s.should == '#<Class:ModuleSpecs::NamedClass>'
+  end
+
+  it 'for objects includes class name and object ID' do
+    obj = ModuleSpecs::NamedClass.new
+    obj.singleton_class.to_s.should =~ /\A#<Class:#<ModuleSpecs::NamedClass:0x\h+>>\z/
   end
 end

spec/ruby/core/module/to_s_spec.rb

@@ -0,0 +1 @@
+fails:Module#to_s for the singleton class of an object of an anonymous class