Update to ruby/spec@21a48d9

25 files changed, 454 insertions, 38 deletions

diff --git a/spec/ruby/command_line/backtrace_limit_spec.rb b/spec/ruby/command_line/backtrace_limit_spec.rb
index c0b243841e..56afa8efef 100644
--- a/spec/ruby/command_line/backtrace_limit_spec.rb
+++ b/spec/ruby/command_line/backtrace_limit_spec.rb
@@ -9,7 +9,7 @@ ruby_version_is "3.0" do
 
       out.should == <<-MSG
 top
-/fixtures/backtrace.rb:2:in `a': unhandled exception
+/fixtures/backtrace.rb:2:in `a': oops (RuntimeError)
 \tfrom /fixtures/backtrace.rb:6:in `b'
 \tfrom /fixtures/backtrace.rb:10:in `c'
 \t ... 2 levels...
@@ -23,7 +23,7 @@ top
 
       out.should == <<-MSG
 full_message
-/fixtures/backtrace.rb:2:in `a': unhandled exception
+/fixtures/backtrace.rb:2:in `a': oops (RuntimeError)
 \tfrom /fixtures/backtrace.rb:6:in `b'
 \tfrom /fixtures/backtrace.rb:10:in `c'
 \t ... 2 levels...
diff --git a/spec/ruby/command_line/dash_upper_w_spec.rb b/spec/ruby/command_line/dash_upper_w_spec.rb
index 1b36a1cc22..cbb040a8dd 100644
--- a/spec/ruby/command_line/dash_upper_w_spec.rb
+++ b/spec/ruby/command_line/dash_upper_w_spec.rb
@@ -19,34 +19,29 @@ describe "The -W command line option with 2" do
   it_behaves_like :command_line_verbose, "-W2"
 end
 
+# Regarding the defaults, see core/warning/element_reference_spec.rb
 ruby_version_is "2.7" do
+  describe "The -W command line option with :deprecated" do
+    it "enables deprecation warnings" do
+      ruby_exe('p Warning[:deprecated]', options: '-W:deprecated').should == "true\n"
+    end
+  end
+
   describe "The -W command line option with :no-deprecated" do
     it "suppresses deprecation warnings" do
-      result = ruby_exe('$; = ""', options: '-w', args: '2>&1')
-      result.should =~ /is deprecated/
-
-      result = ruby_exe('$; = ""', options: '-w -W:no-deprecated', args: '2>&1')
-      result.should == ""
+      ruby_exe('p Warning[:deprecated]', options: '-w -W:no-deprecated').should == "false\n"
     end
   end
 
-  describe "The -W command line option with :no-experimental" do
-    before do
-      ruby_version_is ""..."3.0" do
-        @src = 'case [0, 1]; in [a, b]; end'
-      end
-
-      ruby_version_is "3.0" do
-        @src = 'warn "This is experimental warning.", category: :experimental'
-      end
+  describe "The -W command line option with :experimental" do
+    it "enables experimental warnings" do
+      ruby_exe('p Warning[:experimental]', options: '-W:experimental').should == "true\n"
     end
+  end
 
+  describe "The -W command line option with :no-experimental" do
     it "suppresses experimental warnings" do
-      result = ruby_exe(@src, args: '2>&1')
-      result.should =~ /is experimental/
-
-      result = ruby_exe(@src, options: '-W:no-experimental', args: '2>&1')
-      result.should == ""
+      ruby_exe('p Warning[:experimental]', options: '-w -W:no-experimental').should == "false\n"
     end
   end
 end
diff --git a/spec/ruby/command_line/dash_w_spec.rb b/spec/ruby/command_line/dash_w_spec.rb
index 1d93e0347b..c262df12cc 100644
--- a/spec/ruby/command_line/dash_w_spec.rb
+++ b/spec/ruby/command_line/dash_w_spec.rb
@@ -3,4 +3,10 @@ require_relative 'shared/verbose'
 
 describe "The -w command line option" do
   it_behaves_like :command_line_verbose, "-w"
+
+  ruby_version_is "2.7" do
+    it "enables both deprecated and experimental warnings" do
+      ruby_exe('p Warning[:deprecated]; p Warning[:experimental]', options: '-w').should == "true\ntrue\n"
+    end
+  end
 end
diff --git a/spec/ruby/command_line/fixtures/backtrace.rb b/spec/ruby/command_line/fixtures/backtrace.rb
index 19ad638d35..99acae95c8 100644
--- a/spec/ruby/command_line/fixtures/backtrace.rb
+++ b/spec/ruby/command_line/fixtures/backtrace.rb
@@ -1,5 +1,5 @@
 def a
-  raise
+  raise 'oops'
 end
 
 def b
diff --git a/spec/ruby/core/array/shared/join.rb b/spec/ruby/core/array/shared/join.rb
index c443d9a628..dfdb4ae1e4 100644
--- a/spec/ruby/core/array/shared/join.rb
+++ b/spec/ruby/core/array/shared/join.rb
@@ -124,6 +124,7 @@ describe :array_join_with_default_separator, shared: true do
 
       it "warns" do
         -> { [].join }.should complain(/warning: \$, is set to non-nil value/)
+        -> { [].join(nil) }.should complain(/warning: \$, is set to non-nil value/)
       end
     end
   end
diff --git a/spec/ruby/core/enumerable/grep_spec.rb b/spec/ruby/core/enumerable/grep_spec.rb
index 4e66bb85ea..ac3d3db641 100644
--- a/spec/ruby/core/enumerable/grep_spec.rb
+++ b/spec/ruby/core/enumerable/grep_spec.rb
@@ -59,6 +59,12 @@ describe "Enumerable#grep" do
       ["abc", "def"].grep(/b/).should == ["abc"]
       $&.should == "z"
     end
+
+    it "does not modify Regexp.last_match without block" do
+      "z" =~ /z/ # Reset last match
+      ["abc", "def"].grep(/b/).should == ["abc"]
+      Regexp.last_match[0].should == "z"
+    end
   end
 
   describe "with a block" do
diff --git a/spec/ruby/core/enumerable/grep_v_spec.rb b/spec/ruby/core/enumerable/grep_v_spec.rb
index 8cae3ac618..892640efa4 100644
--- a/spec/ruby/core/enumerable/grep_v_spec.rb
+++ b/spec/ruby/core/enumerable/grep_v_spec.rb
@@ -39,6 +39,12 @@ describe "Enumerable#grep_v" do
       ["abc", "def"].grep_v(/e/).should == ["abc"]
       $&.should == "z"
     end
+
+    it "does not modify Regexp.last_match without block" do
+      "z" =~ /z/ # Reset last match
+      ["abc", "def"].grep_v(/e/).should == ["abc"]
+      Regexp.last_match[0].should == "z"
+    end
   end
 
   describe "without block" do
diff --git a/spec/ruby/core/fiber/blocking_spec.rb b/spec/ruby/core/fiber/blocking_spec.rb
new file mode 100644
index 0000000000..5ae5fbd577
--- /dev/null
+++ b/spec/ruby/core/fiber/blocking_spec.rb
@@ -0,0 +1,62 @@
+require_relative '../../spec_helper'
+require_relative 'shared/blocking'
+
+ruby_version_is "3.0" do
+  require "fiber"
+
+  describe "Fiber.blocking?" do
+    it_behaves_like :non_blocking_fiber, -> { Fiber.blocking? }
+
+    context "when fiber is blocking" do
+      context "root Fiber of the main thread" do
+        it "returns 1 for blocking: true" do
+          fiber = Fiber.new(blocking: true) { Fiber.blocking? }
+          blocking = fiber.resume
+
+          blocking.should == 1
+        end
+      end
+
+      context "root Fiber of a new thread" do
+        it "returns 1 for blocking: true" do
+          thread = Thread.new do
+            fiber = Fiber.new(blocking: true) { Fiber.blocking? }
+            blocking = fiber.resume
+
+            blocking.should == 1
+          end
+
+          thread.join
+        end
+      end
+    end
+  end
+
+  describe "Fiber#blocking?" do
+    it_behaves_like :non_blocking_fiber, -> { Fiber.current.blocking? }
+
+    context "when fiber is blocking" do
+      context "root Fiber of the main thread" do
+        it "returns true for blocking: true" do
+          fiber = Fiber.new(blocking: true) { Fiber.current.blocking? }
+          blocking = fiber.resume
+
+          blocking.should == true
+        end
+      end
+
+      context "root Fiber of a new thread" do
+        it "returns true for blocking: true" do
+          thread = Thread.new do
+            fiber = Fiber.new(blocking: true) { Fiber.current.blocking? }
+            blocking = fiber.resume
+
+            blocking.should == true
+          end
+
+          thread.join
+        end
+      end
+    end
+  end
+end
diff --git a/spec/ruby/core/fiber/shared/blocking.rb b/spec/ruby/core/fiber/shared/blocking.rb
new file mode 100644
index 0000000000..21707e1ea7
--- /dev/null
+++ b/spec/ruby/core/fiber/shared/blocking.rb
@@ -0,0 +1,41 @@
+describe :non_blocking_fiber, shared: true do
+  context "root Fiber of the main thread" do
+    it "returns false" do
+      fiber = Fiber.new { @method.call }
+      blocking = fiber.resume
+
+      blocking.should == false
+    end
+
+    it "returns false for blocking: false" do
+      fiber = Fiber.new(blocking: false) { @method.call }
+      blocking = fiber.resume
+
+      blocking.should == false
+    end
+  end
+
+  context "root Fiber of a new thread" do
+    it "returns false" do
+      thread = Thread.new do
+        fiber = Fiber.new { @method.call }
+        blocking = fiber.resume
+
+        blocking.should == false
+      end
+
+      thread.join
+    end
+
+    it "returns false for blocking: false" do
+      thread = Thread.new do
+        fiber = Fiber.new(blocking: false) { @method.call }
+        blocking = fiber.resume
+
+        blocking.should == false
+      end
+
+      thread.join
+    end
+  end
+end
diff --git a/spec/ruby/core/gc/auto_compact_spec.rb b/spec/ruby/core/gc/auto_compact_spec.rb
new file mode 100644
index 0000000000..d77ed44452
--- /dev/null
+++ b/spec/ruby/core/gc/auto_compact_spec.rb
@@ -0,0 +1,19 @@
+require_relative '../../spec_helper'
+
+ruby_version_is "3.0" do
+  describe "GC.auto_compact" do
+    before :each do
+      @default = GC.auto_compact
+    end
+
+    after :each do
+      GC.auto_compact = @default
+    end
+
+    it "can set and get a boolean value" do
+      original = GC.auto_compact
+      GC.auto_compact = !original
+      GC.auto_compact.should == !original
+    end
+  end
+end
diff --git a/spec/ruby/core/io/nonblock_spec.rb b/spec/ruby/core/io/nonblock_spec.rb
new file mode 100644
index 0000000000..e81ac10c58
--- /dev/null
+++ b/spec/ruby/core/io/nonblock_spec.rb
@@ -0,0 +1,70 @@
+require_relative '../../spec_helper'
+
+platform_is_not :windows do
+  describe "IO#nonblock?" do
+    before :all do
+      require 'io/nonblock'
+    end
+
+    it "returns false for a file by default" do
+      File.open(__FILE__) do |f|
+        f.nonblock?.should == false
+      end
+    end
+
+    ruby_version_is ""..."3.0" do
+      it "returns false for pipe by default" do
+        r, w = IO.pipe
+        begin
+          r.nonblock?.should == false
+          w.nonblock?.should == false
+        ensure
+          r.close
+          w.close
+        end
+      end
+
+      it "returns false for socket by default" do
+        require 'socket'
+        TCPServer.open(0) do |socket|
+          socket.nonblock?.should == false
+        end
+      end
+    end
+
+    ruby_version_is "3.0" do
+      it "returns true for pipe by default" do
+        r, w = IO.pipe
+        begin
+          r.nonblock?.should == true
+          w.nonblock?.should == true
+        ensure
+          r.close
+          w.close
+        end
+      end
+
+      it "returns true for socket by default" do
+        require 'socket'
+        TCPServer.open(0) do |socket|
+          socket.nonblock?.should == true
+        end
+      end
+    end
+  end
+
+  describe "IO#nonblock=" do
+    before :all do
+      require 'io/nonblock'
+    end
+
+    it "changes the IO to non-blocking mode" do
+      File.open(__FILE__) do |f|
+        f.nonblock = true
+        f.nonblock?.should == true
+        f.nonblock = false
+        f.nonblock?.should == false
+      end
+    end
+  end
+end
diff --git a/spec/ruby/core/kernel/lambda_spec.rb b/spec/ruby/core/kernel/lambda_spec.rb
index 9a960f3589..2aa4d4f2fb 100644
--- a/spec/ruby/core/kernel/lambda_spec.rb
+++ b/spec/ruby/core/kernel/lambda_spec.rb
@@ -135,4 +135,16 @@ describe "Kernel.lambda" do
     klass.new.lambda { 42 }.should be_an_instance_of Proc
     klass.new.ret.should == 1
   end
+
+  ruby_version_is "3.0" do
+    context "when called without a literal block" do
+      it "warns when proc isn't a lambda" do
+        -> { lambda(&proc{}) }.should complain("#{__FILE__}:#{__LINE__}: warning: lambda without a literal block is deprecated; use the proc without lambda instead\n")
+      end
+
+      it "doesn't warn when proc is lambda" do
+        -> { lambda(&lambda{}) }.should_not complain(verbose: true)
+      end
+    end
+  end
 end
diff --git a/spec/ruby/core/kernel/open_spec.rb b/spec/ruby/core/kernel/open_spec.rb
index 8d936d8ca0..569f2f6a7f 100644
--- a/spec/ruby/core/kernel/open_spec.rb
+++ b/spec/ruby/core/kernel/open_spec.rb
@@ -148,6 +148,18 @@ describe "Kernel#open" do
       ruby_exe(code, args: "2>&1").should == "true\n"
     end
   end
+
+  ruby_version_is "3.0" do
+    it "is not redefined by open-uri" do
+      code = <<~RUBY
+        before = Kernel.instance_method(:open)
+        require 'open-uri'
+        after = Kernel.instance_method(:open)
+        p before == after
+      RUBY
+      ruby_exe(code, args: "2>&1").should == "true\n"
+    end
+  end
 end
 
 describe "Kernel.open" do
diff --git a/spec/ruby/core/module/deprecate_constant_spec.rb b/spec/ruby/core/module/deprecate_constant_spec.rb
index 7bcced981b..faacbea03e 100644
--- a/spec/ruby/core/module/deprecate_constant_spec.rb
+++ b/spec/ruby/core/module/deprecate_constant_spec.rb
@@ -9,7 +9,6 @@ describe "Module#deprecate_constant" do
     @module::PRIVATE = @value
     @module.private_constant :PRIVATE
     @module.deprecate_constant :PRIVATE
-    @pattern = /deprecated/
   end
 
   describe "when accessing the deprecated module" do
@@ -19,7 +18,7 @@ describe "Module#deprecate_constant" do
       value = nil
       -> {
         value = @module::PUBLIC1
-      }.should complain(@pattern)
+      }.should complain(/warning: constant .+::PUBLIC1 is deprecated/)
       value.should equal(@value)
 
       -> { @module::PRIVATE }.should raise_error(NameError)
@@ -28,16 +27,30 @@ describe "Module#deprecate_constant" do
     it "warns with a message" do
       @module.deprecate_constant :PUBLIC1
 
-      -> { @module::PUBLIC1 }.should complain(@pattern)
-      -> { @module.const_get :PRIVATE }.should complain(@pattern)
+      -> { @module::PUBLIC1 }.should complain(/warning: constant .+::PUBLIC1 is deprecated/)
+      -> { @module.const_get :PRIVATE }.should complain(/warning: constant .+::PRIVATE is deprecated/)
+    end
+
+    ruby_version_is '2.7' do
+      it "does not warn if Warning[:deprecated] is false" do
+        @module.deprecate_constant :PUBLIC1
+
+        deprecated = Warning[:deprecated]
+        begin
+          Warning[:deprecated] = false
+          -> { @module::PUBLIC1 }.should_not complain
+        ensure
+          Warning[:deprecated] = deprecated
+        end
+      end
     end
   end
 
   it "accepts multiple symbols and strings as constant names" do
     @module.deprecate_constant "PUBLIC1", :PUBLIC2
 
-    -> { @module::PUBLIC1 }.should complain(@pattern)
-    -> { @module::PUBLIC2 }.should complain(@pattern)
+    -> { @module::PUBLIC1 }.should complain(/warning: constant .+::PUBLIC1 is deprecated/)
+    -> { @module::PUBLIC2 }.should complain(/warning: constant .+::PUBLIC2 is deprecated/)
   end
 
   it "returns self" do
diff --git a/spec/ruby/core/module/private_class_method_spec.rb b/spec/ruby/core/module/private_class_method_spec.rb
index e35b50d986..407779cccc 100644
--- a/spec/ruby/core/module/private_class_method_spec.rb
+++ b/spec/ruby/core/module/private_class_method_spec.rb
@@ -78,4 +78,16 @@ describe "Module#private_class_method" do
       end
     end.should raise_error(NameError)
   end
+
+  ruby_version_is "3.0" do
+    context "when single argument is passed and is an array" do
+      it "sets the visibility of the given methods to private" do
+        c = Class.new do
+          def self.foo() "foo" end
+          private_class_method [:foo]
+        end
+        -> { c.foo }.should raise_error(NoMethodError)
+      end
+    end
+  end
 end
diff --git a/spec/ruby/core/module/public_class_method_spec.rb b/spec/ruby/core/module/public_class_method_spec.rb
index c09cc64863..b5d76e7b7a 100644
--- a/spec/ruby/core/module/public_class_method_spec.rb
+++ b/spec/ruby/core/module/public_class_method_spec.rb
@@ -77,4 +77,20 @@ describe "Module#public_class_method" do
       end
     end.should raise_error(NameError)
   end
+
+  ruby_version_is "3.0" do
+    context "when single argument is passed and is an array" do
+      it "makes a class method public" do
+        c = Class.new do
+          class << self
+            private
+            def foo() "foo" end
+          end
+          public_class_method [:foo]
+        end
+
+        c.foo.should == "foo"
+      end
+    end
+  end
 end
diff --git a/spec/ruby/core/random/default_spec.rb b/spec/ruby/core/random/default_spec.rb
index a709eddd53..db444d203d 100644
--- a/spec/ruby/core/random/default_spec.rb
+++ b/spec/ruby/core/random/default_spec.rb
@@ -1,7 +1,6 @@
 require_relative '../../spec_helper'
 
 describe "Random::DEFAULT" do
-
   it "returns a random number generator" do
     suppress_warning do
       Random::DEFAULT.should respond_to(:rand)
diff --git a/spec/ruby/core/string/encode_spec.rb b/spec/ruby/core/string/encode_spec.rb
index ae641b2110..5604ab7210 100644
--- a/spec/ruby/core/string/encode_spec.rb
+++ b/spec/ruby/core/string/encode_spec.rb
@@ -67,10 +67,52 @@ describe "String#encode" do
       "\rfoo".encode(universal_newline: true).should == "\nfoo"
     end
 
-    it "replaces invalid encoding" do
-      encoded = "ち\xE3\x81\xFF".encode("UTF-16LE", invalid: :replace, replace: "?")
-      encoded.should == "\u3061??".encode("UTF-16LE")
-      encoded.encode("UTF-8").should == "ち??"
+    it "replaces invalid encoding in source with default replacement" do
+      encoded = "ち\xE3\x81\xFF".encode("UTF-16LE", invalid: :replace)
+      encoded.should == "\u3061\ufffd\ufffd".encode("UTF-16LE")
+      encoded.encode("UTF-8").should == "ち\ufffd\ufffd"
+    end
+
+    it "replaces invalid encoding in source with a specified replacement" do
+      encoded = "ち\xE3\x81\xFF".encode("UTF-16LE", invalid: :replace, replace: "foo")
+      encoded.should == "\u3061foofoo".encode("UTF-16LE")
+      encoded.encode("UTF-8").should == "ちfoofoo"
+    end
+
+    it "replaces invalid encoding in source using a specified replacement even when a fallback is given" do
+      encoded = "ち\xE3\x81\xFF".encode("UTF-16LE", invalid: :replace, replace: "foo", fallback: -> c { "bar" })
+      encoded.should == "\u3061foofoo".encode("UTF-16LE")
+      encoded.encode("UTF-8").should == "ちfoofoo"
+    end
+
+    it "replaces undefined encoding in destination with default replacement" do
+      encoded = "B\ufffd".encode(Encoding::US_ASCII, undef: :replace)
+      encoded.should == "B?".encode(Encoding::US_ASCII)
+      encoded.encode("UTF-8").should == "B?"
+    end
+
+    it "replaces undefined encoding in destination with a specified replacement" do
+      encoded = "B\ufffd".encode(Encoding::US_ASCII, undef: :replace, replace: "foo")
+      encoded.should == "Bfoo".encode(Encoding::US_ASCII)
+      encoded.encode("UTF-8").should == "Bfoo"
+    end
+
+    it "replaces undefined encoding in destination with a specified replacement even if a fallback is given" do
+      encoded = "B\ufffd".encode(Encoding::US_ASCII, undef: :replace, replace: "foo", fallback: proc {|x| "bar"})
+      encoded.should == "Bfoo".encode(Encoding::US_ASCII)
+      encoded.encode("UTF-8").should == "Bfoo"
+    end
+
+    it "replaces undefined encoding in destination using a fallback proc" do
+      encoded = "B\ufffd".encode(Encoding::US_ASCII, fallback: proc {|x| "bar"})
+      encoded.should == "Bbar".encode(Encoding::US_ASCII)
+      encoded.encode("UTF-8").should == "Bbar"
+    end
+
+    it "replaces invalid encoding in source using replace even when fallback is given as proc" do
+      encoded = "ち\xE3\x81\xFF".encode("UTF-16LE", invalid: :replace, replace: "foo", fallback: proc {|x| "bar"})
+      encoded.should == "\u3061foofoo".encode("UTF-16LE")
+      encoded.encode("UTF-8").should == "ちfoofoo"
     end
   end
 
diff --git a/spec/ruby/core/symbol/to_proc_spec.rb b/spec/ruby/core/symbol/to_proc_spec.rb
index e9261e6cdf..47f2a939ab 100644
--- a/spec/ruby/core/symbol/to_proc_spec.rb
+++ b/spec/ruby/core/symbol/to_proc_spec.rb
@@ -47,7 +47,9 @@ describe "Symbol#to_proc" do
   end
 
   it "raises an ArgumentError when calling #call on the Proc without receiver" do
-    -> { :object_id.to_proc.call }.should raise_error(ArgumentError, "no receiver given")
+    -> {
+      :object_id.to_proc.call
+    }.should raise_error(ArgumentError, /no receiver given|wrong number of arguments \(given 0, expected 1\+\)/)
   end
 
   it "passes along the block passed to Proc#call" do
diff --git a/spec/ruby/core/thread/ignore_deadlock_spec.rb b/spec/ruby/core/thread/ignore_deadlock_spec.rb
new file mode 100644
index 0000000000..53cc2a7f5b
--- /dev/null
+++ b/spec/ruby/core/thread/ignore_deadlock_spec.rb
@@ -0,0 +1,21 @@
+require_relative '../../spec_helper'
+
+ruby_version_is "3.0" do
+  describe "Thread.ignore_deadlock" do
+    it "returns false by default" do
+      Thread.ignore_deadlock.should == false
+    end
+  end
+
+  describe "Thread.ignore_deadlock=" do
+    it "changes the value of Thread.ignore_deadlock" do
+      ignore_deadlock = Thread.ignore_deadlock
+      Thread.ignore_deadlock = true
+      begin
+        Thread.ignore_deadlock.should == true
+      ensure
+        Thread.ignore_deadlock = ignore_deadlock
+      end
+    end
+  end
+end
diff --git a/spec/ruby/core/warning/element_reference_spec.rb b/spec/ruby/core/warning/element_reference_spec.rb
index c3bf06a95b..a346cf535b 100644
--- a/spec/ruby/core/warning/element_reference_spec.rb
+++ b/spec/ruby/core/warning/element_reference_spec.rb
@@ -1,10 +1,12 @@
 require_relative '../../spec_helper'
 
-ruby_version_is '2.7.2' do
+ruby_version_is '2.7' do
   describe "Warning.[]" do
-    it "returns default values for categories :deprecated and :experimental" do
-      ruby_exe('p Warning[:deprecated]').chomp.should == "false"
-      ruby_exe('p Warning[:experimental]').chomp.should == "true"
+    ruby_version_is '2.7.2' do
+      it "returns default values for categories :deprecated and :experimental" do
+        ruby_exe('p Warning[:deprecated]').chomp.should == "false"
+        ruby_exe('p Warning[:experimental]').chomp.should == "true"
+      end
     end
 
     it "raises for unknown category" do
diff --git a/spec/ruby/language/class_variable_spec.rb b/spec/ruby/language/class_variable_spec.rb
index dffab47a6b..9a4b36e82b 100644
--- a/spec/ruby/language/class_variable_spec.rb
+++ b/spec/ruby/language/class_variable_spec.rb
@@ -82,3 +82,29 @@ describe 'A class variable definition' do
     c.class_variable_get(:@@cv).should == :next
   end
 end
+
+ruby_version_is "3.0" do
+  describe 'Accessing a class variable' do
+    it "raises a RuntimeError when accessed from the toplevel scope (not in some module or class)" do
+      -> {
+        eval "@@cvar_toplevel1"
+      }.should raise_error(RuntimeError, 'class variable access from toplevel')
+      -> {
+        eval "@@cvar_toplevel2 = 2"
+      }.should raise_error(RuntimeError, 'class variable access from toplevel')
+    end
+
+    it "raises a RuntimeError when a class variable is overtaken in an ancestor class" do
+      parent = Class.new()
+      subclass = Class.new(parent)
+      subclass.class_variable_set(:@@cvar_overtaken, :subclass)
+      parent.class_variable_set(:@@cvar_overtaken, :parent)
+
+      -> {
+        subclass.class_variable_get(:@@cvar_overtaken)
+      }.should raise_error(RuntimeError, /class variable @@cvar_overtaken of .+ is overtaken by .+/)
+
+      parent.class_variable_get(:@@cvar_overtaken).should == :parent
+    end
+  end
+end
diff --git a/spec/ruby/language/numbered_parameters_spec.rb b/spec/ruby/language/numbered_parameters_spec.rb
index cd1ddf4555..838822b2d6 100644
--- a/spec/ruby/language/numbered_parameters_spec.rb
+++ b/spec/ruby/language/numbered_parameters_spec.rb
@@ -80,6 +80,20 @@ ruby_version_is "2.7" do
       -> { eval("['a'].map { |x| _1 }") }.should raise_error(SyntaxError, /ordinary parameter is defined/)
     end
 
+    describe "assigning to a numbered parameter" do
+      ruby_version_is '2.7'...'3.0' do
+        it "warns" do
+          -> { eval("proc { _1 = 0 }") }.should complain(/warning: `_1' is reserved for numbered parameter; consider another name/)
+        end
+      end
+
+      ruby_version_is '3.0' do
+        it "raises SyntaxError" do
+          -> { eval("proc { _1 = 0 }") }.should raise_error(SyntaxError, /_1 is reserved for numbered parameter/)
+        end
+      end
+    end
+
     it "affects block arity" do
       -> { _1 }.arity.should == 1
       -> { _2 }.arity.should == 2
diff --git a/spec/ruby/language/safe_spec.rb b/spec/ruby/language/safe_spec.rb
index 062381d729..89830a2069 100644
--- a/spec/ruby/language/safe_spec.rb
+++ b/spec/ruby/language/safe_spec.rb
@@ -106,4 +106,14 @@ describe "The $SAFE variable" do
       }.should complain(/\$SAFE will become a normal global variable in Ruby 3.0/)
     end
   end
+
+  ruby_version_is "3.0" do
+    it "$SAFE is a regular global variable" do
+      $SAFE.should == nil
+      $SAFE = 42
+      $SAFE.should == 42
+    ensure
+      $SAFE = nil
+    end
+  end
 end
diff --git a/spec/ruby/language/variables_spec.rb b/spec/ruby/language/variables_spec.rb
index 7d6969e659..699187335c 100644
--- a/spec/ruby/language/variables_spec.rb
+++ b/spec/ruby/language/variables_spec.rb
@@ -822,3 +822,32 @@ describe 'Allowed characters' do
     result.should == 1
   end
 end
+
+describe "Instance variables" do
+  context "when instance variable is uninitialized" do
+    ruby_version_is ""..."3.0" do
+      it "warns about accessing uninitialized instance variable" do
+        obj = Object.new
+        def obj.foobar; a = @a; end
+
+        -> { obj.foobar }.should complain(/warning: instance variable @a not initialized/, verbose: true)
+      end
+    end
+
+    ruby_version_is "3.0" do
+      it "doesn't warn about accessing uninitialized instance variable" do
+        obj = Object.new
+        def obj.foobar; a = @a; end
+
+        -> { obj.foobar }.should_not complain(verbose: true)
+      end
+    end
+
+    it "doesn't warn at lazy initialization" do
+      obj = Object.new
+      def obj.foobar; @a ||= 42; end
+
+      -> { obj.foobar }.should_not complain(verbose: true)
+    end
+  end
+end