Import language/pattern_matching_spec

We are finally able to run the first few tests.

spec/language/pattern_matching/3.1.rb

@@ -0,0 +1,76 @@
+describe "Pattern matching" do
+  before :each do
+    ScratchPad.record []
+  end
+
+  # NATFIXME: Handle Prism::CaseMatchNode
+  describe "Ruby 3.1 improvements" do
+    ruby_version_is "3.1" do
+      xit "can omit parentheses in one line pattern matching" do
+        #[1, 2] => a, b
+        #[a, b].should == [1, 2]
+
+        #{a: 1} => a:
+        #a.should == 1
+      end
+
+      xit "supports pinning instance variables" do
+        #@a = /a/
+        #case 'abc'
+        #in ^@a
+          #true
+        #end.should == true
+      end
+
+      xit "supports pinning class variables" do
+        #result = nil
+        #Module.new do
+          #result = module_eval(<<~RUBY)
+            #@@a = 0..10
+
+            #case 2
+            #in ^@@a
+              #true
+            #end
+          #RUBY
+        #end
+
+        #result.should == true
+      end
+
+      xit "supports pinning global variables" do
+        #$a = /a/
+        #case 'abc'
+        #in ^$a
+          #true
+        #end.should == true
+      end
+
+      xit "supports pinning expressions" do
+        #case 'abc'
+        #in ^(/a/)
+          #true
+        #end.should == true
+
+        #case 0
+        #in ^(0 + 0)
+          #true
+        #end.should == true
+      end
+
+      xit "supports pinning expressions in array pattern" do
+        #case [3]
+        #in [^(1 + 2)]
+          #true
+        #end.should == true
+      end
+
+      xit "supports pinning expressions in hash pattern" do
+        #case {name: '2.6', released_at: Time.new(2018, 12, 25)}
+        #in {released_at: ^(Time.new(2010)..Time.new(2020))}
+          #true
+        #end.should == true
+      end
+    end
+  end
+end