Implement Kernel#raise cause parameter

Author: bjfish

core/kernel/raise_spec.rb

@@ -27,6 +27,27 @@
 
     ScratchPad.recorded.should be_nil
   end
+
+  ruby_version_is "2.6" do
+    it "accepts a cause keyword argument that sets the cause" do
+      cause = StandardError.new
+      -> { raise("error", cause: cause) }.should raise_error(RuntimeError) { |e| e.cause.should == cause }
+    end
+
+    it "accepts a cause keyword argument that overrides the last exception" do
+      begin
+        raise "first raise"
+      rescue => e
+        cause = StandardError.new
+        -> { raise("error", cause: cause) }.should raise_error(RuntimeError) { |e| e.cause.should == cause }
+      end
+    end
+
+    it "raises an ArgumentError when only cause is given" do
+      cause = StandardError.new
+      -> { raise(cause: cause) }.should raise_error(ArgumentError)
+    end
+  end
 end
 
 describe "Kernel#raise" do