1 files changed, 13 insertions, 2 deletions
diff --git a/spec/ruby/core/array/sum_spec.rb b/spec/ruby/core/array/sum_spec.rb
index 1f1d6b2f14..cd4ba4c2d8 100644
--- a/spec/ruby/core/array/sum_spec.rb
+++ b/spec/ruby/core/array/sum_spec.rb
@@ -10,6 +10,10 @@ describe "Array#sum" do
     [1, 2, 3].sum { |i| i * 10 }.should == 60
   end
 
+  it "doesn't apply the block init" do
+    [1, 2, 3].sum(1) { |i| i * 10 }.should == 61
+  end
+
   # https://bugs.ruby-lang.org/issues/12217
   # https://github.com/ruby/ruby/blob/master/doc/ChangeLog/ChangeLog-2.4.0#L6208-L6214
   it "uses Kahan's compensated summation algorithm for precise sum of float numbers" do
@@ -56,11 +60,11 @@ describe "Array#sum" do
   end
 
   it 'raises TypeError if any element are not numeric' do
-    -> { ["a"].sum }.should raise_error(TypeError)
+    -> { ["a"].sum }.should.raise(TypeError)
   end
 
   it 'raises TypeError if any element cannot be added to init value' do
-    -> { [1].sum([]) }.should raise_error(TypeError)
+    -> { [1].sum([]) }.should.raise(TypeError)
   end
 
   it "calls + to sum the elements" do
@@ -69,6 +73,13 @@ describe "Array#sum" do
     a.should_receive(:+).with(b).and_return(42)
     [b].sum(a).should == 42
   end
+
+  it "calls + on the init value" do
+    a = mock("a")
+    b = mock("b")
+    a.should_receive(:+).with(42).and_return(b)
+    [42].sum(a).should == b
+  end
 end
 
 describe "Array#sum" do