1 files changed, 81 insertions, 0 deletions
diff --git a/spec/ruby/core/enumerable/max_by_spec.rb b/spec/ruby/core/enumerable/max_by_spec.rb
new file mode 100644
index 0000000000..4058cf0a40
--- /dev/null
+++ b/spec/ruby/core/enumerable/max_by_spec.rb
@@ -0,0 +1,81 @@
+require File.expand_path('../../../spec_helper', __FILE__)
+require File.expand_path('../fixtures/classes', __FILE__)
+require File.expand_path('../shared/enumerable_enumeratorized', __FILE__)
+
+describe "Enumerable#max_by" do
+  it "returns an enumerator if no block" do
+    EnumerableSpecs::Numerous.new(42).max_by.should be_an_instance_of(Enumerator)
+  end
+
+  it "returns nil if #each yields no objects" do
+    EnumerableSpecs::Empty.new.max_by {|o| o.nonesuch }.should == nil
+  end
+
+  it "returns the object for whom the value returned by block is the largest" do
+    EnumerableSpecs::Numerous.new(*%w[1 2 3]).max_by {|obj| obj.to_i }.should == '3'
+    EnumerableSpecs::Numerous.new(*%w[three five]).max_by {|obj| obj.length }.should == 'three'
+  end
+
+  it "returns the object that appears first in #each in case of a tie" do
+    a, b, c = '1', '2', '2'
+    EnumerableSpecs::Numerous.new(a, b, c).max_by {|obj| obj.to_i }.should equal(b)
+  end
+
+  it "uses max.<=>(current) to determine order" do
+    a, b, c = (1..3).map{|n| EnumerableSpecs::ReverseComparable.new(n)}
+
+    # Just using self here to avoid additional complexity
+    EnumerableSpecs::Numerous.new(a, b, c).max_by {|obj| obj }.should == a
+  end
+
+  it "is able to return the maximum for enums that contain nils" do
+    enum = EnumerableSpecs::Numerous.new(nil, nil, true)
+    enum.max_by {|o| o.nil? ? 0 : 1 }.should == true
+    enum.max_by {|o| o.nil? ? 1 : 0 }.should == nil
+  end
+
+  it "gathers whole arrays as elements when each yields multiple" do
+    multi = EnumerableSpecs::YieldsMulti.new
+    multi.max_by {|e| e.size}.should == [6, 7, 8, 9]
+  end
+
+  it_behaves_like :enumerable_enumeratorized_with_origin_size, :max_by
+
+  context "when called with an argument n" do
+    before :each do
+      @enum = EnumerableSpecs::Numerous.new(101, 55, 1, 20, 33, 500, 60)
+    end
+
+    context "without a block" do
+      it "returns an enumerator" do
+        @enum.max_by(2).should be_an_instance_of(Enumerator)
+      end
+    end
+
+    context "with a block" do
+      it "returns an array containing the maximum n elements based on the block's value" do
+        result = @enum.max_by(3) { |i| i.to_s }
+        result.should == [60, 55, 500]
+      end
+
+      context "on a enumerable of length x where x < n" do
+        it "returns an array containing the maximum n elements of length n" do
+          result = @enum.max_by(500) { |i| i.to_s }
+          result.length.should == 7
+        end
+      end
+
+      context "when n is negative" do
+        it "raises an ArgumentError" do
+          lambda { @enum.max_by(-1) { |i| i.to_s } }.should raise_error(ArgumentError)
+        end
+      end
+    end
+
+    context "when n is nil" do
+      it "returns the maximum element" do
+        @enum.max_by(nil) { |i| i.to_s }.should == 60
+      end
+    end
+  end
+end