1 files changed, 44 insertions, 0 deletions
diff --git a/spec/ruby/core/array/sum_spec.rb b/spec/ruby/core/array/sum_spec.rb
new file mode 100644
index 0000000000..6548655c35
--- /dev/null
+++ b/spec/ruby/core/array/sum_spec.rb
@@ -0,0 +1,44 @@
+require File.expand_path('../../../spec_helper', __FILE__)
+
+ruby_version_is '2.4' do
+  describe "Array#sum" do
+    it "returns the sum of elements" do
+      [1, 2, 3].sum.should == 6
+    end
+
+    it "applies a block to each element before adding if it's given" do
+      [1, 2, 3].sum { |i| i * 10 }.should == 60
+    end
+
+    it "returns init value if array is empty" do
+      [].sum(-1).should == -1
+    end
+
+    it "returns 0 if array is empty and init is omitted" do
+      [].sum.should == 0
+    end
+
+    it "adds init value to the sum of elemens" do
+      [1, 2, 3].sum(10).should == 16
+    end
+
+    it "can be used for non-numeric objects by providing init value" do
+      ["a", "b", "c"].sum("").should == "abc"
+    end
+
+    it 'raises TypeError if any element are not numeric' do
+      lambda { ["a"].sum }.should raise_error(TypeError)
+    end
+
+    it 'raises TypeError if any element cannot be added to init value' do
+      lambda { [1].sum([]) }.should raise_error(TypeError)
+    end
+
+    it "calls + to sum the elements" do
+      a = mock("a")
+      b = mock("b")
+      a.should_receive(:+).with(b).and_return(42)
+      [b].sum(a).should == 42
+    end
+  end
+end