Add specs for #each passing source yields by block arity (Enumerator and Lazy)

Unlike the Enumerable collection methods, which pack yielded source values via
rb_enum_values_pack() (0 args -> nil, 1 arg -> the value, N args -> Array), #each
passes them to the block by ordinary block arity (rb_yield_values2() in CRuby):
a single-argument block receives the first value, a multi-argument block
destructures, and a splat block gathers them.

Author: sampokuokkanen

core/enumerator/each_spec.rb

@@ -1,6 +1,21 @@
 require_relative '../../spec_helper'
+require_relative 'shared/each'
 
 describe "Enumerator#each" do
+  describe "passing source-yielded arguments to the block" do
+    before :each do
+      @object = -> e { e }
+    end
+    it_behaves_like :enum_each, nil
+  end
+
+  describe "passing source-yielded arguments to the block (lazy)" do
+    before :each do
+      @object = -> e { e.lazy }
+    end
+    it_behaves_like :enum_each, nil
+  end
+
   before :each do
     object_each_with_arguments = Object.new
     def object_each_with_arguments.each_with_arguments(arg, *args)

core/enumerator/shared/each.rb

@@ -0,0 +1,46 @@
+# #each passes source-yielded values to the block by ordinary block arity
+# (rb_yield_values2 semantics in CRuby), unlike the Enumerable collection methods
+# which pack them via rb_enum_values_pack() (see enumerable/shared/value_packing.rb).
+describe :enum_each, shared: true do
+  # @object must be set to a Proc that wraps an Enumerator into the receiver
+  # under test (e.g. -> e { e } for Enumerator#each, -> e { e.lazy } for Lazy#each).
+  describe "with a source that yields multiple values" do
+    before :each do
+      @enum = @object.call(Enumerator.new { |y| y.yield 1, 2; y.yield 3, 4 })
+    end
+
+    it "yields the first value to a single-argument block" do
+      collected = []
+      @enum.each { |x| collected << x }
+      collected.should == [1, 3]
+    end
+
+    it "yields each value to a multi-argument block" do
+      collected = []
+      @enum.each { |x, y| collected << [x, y] }
+      collected.should == [[1, 2], [3, 4]]
+    end
+
+    it "gathers the values for a splat block" do
+      collected = []
+      @enum.each { |*args| collected << args }
+      collected.should == [[1, 2], [3, 4]]
+    end
+  end
+
+  describe "with a source that yields a single value" do
+    it "yields the value to a single-argument block" do
+      collected = []
+      @object.call(Enumerator.new { |y| y.yield 7; y.yield 8 }).each { |x| collected << x }
+      collected.should == [7, 8]
+    end
+  end
+
+  describe "with a source that yields no value" do
+    it "yields nil to a single-argument block" do
+      collected = []
+      @object.call(Enumerator.new { |y| y.yield; y.yield }).each { |x| collected << x }
+      collected.should == [nil, nil]
+    end
+  end
+end