Expand Symbol#to_proc specs to be clearer

spec/ruby/core/symbol/to_proc_spec.rb

@@ -12,22 +12,44 @@ describe "Symbol#to_proc" do
     :to_s.to_proc.call(obj).should == "Received #to_s"
   end
 
-  expected_arity = ruby_version_is("2.8") {-2} || -1
-  it "produces a proc with arity #{expected_arity}" do
-    pr = :to_s.to_proc
-    pr.arity.should == expected_arity
+  ruby_version_is ""..."2.8" do
+    it "returns a Proc with #lambda? false" do
+      pr = :to_s.to_proc
+      pr.lambda?.should == false
+    end
+
+    it "produces a Proc with arity -1" do
+      pr = :to_s.to_proc
+      pr.arity.should == -1
+    end
+
+    it "produces a Proc that always returns [[:rest]] for #parameters" do
+      pr = :to_s.to_proc
+      pr.parameters.should == [[:rest]]
+    end
+  end
+
+  ruby_version_is "2.8" do
+    it "returns a Proc with #lambda? true" do
+      pr = :to_s.to_proc
+      pr.lambda?.should == true
+    end
+
+    it "produces a Proc with arity -2" do
+      pr = :to_s.to_proc
+      pr.arity.should == -2
+    end
+
+    it "produces a Proc that always returns [[:req], [:rest]] for #parameters" do
+      pr = :to_s.to_proc
+      pr.parameters.should == [[:req], [:rest]]
+    end
   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")
   end
 
-  expected_parameters = ruby_version_is("2.8") {[[:req], [:rest]]} || [[:rest]]
-  it "produces a proc that always returns #{expected_parameters} for #parameters" do
-    pr = :to_s.to_proc
-    pr.parameters.should == expected_parameters
-  end
-
   it "passes along the block passed to Proc#call" do
     klass = Class.new do
       def m