1 files changed, 78 insertions, 0 deletions
diff --git a/spec/ruby/core/hash/shift_spec.rb b/spec/ruby/core/hash/shift_spec.rb
new file mode 100644
index 0000000000..6095d2e55f
--- /dev/null
+++ b/spec/ruby/core/hash/shift_spec.rb
@@ -0,0 +1,78 @@
+require_relative '../../spec_helper'
+require_relative 'fixtures/classes'
+
+describe "Hash#shift" do
+  it "removes a pair from hash and return it" do
+    h = { a: 1, b: 2, "c" => 3, nil => 4, [] => 5 }
+    h2 = h.dup
+
+    h.size.times do |i|
+      r = h.shift
+      r.should.is_a?(Array)
+      h2[r.first].should == r.last
+      h.size.should == h2.size - i - 1
+    end
+
+    h.should == {}
+  end
+
+  # MRI explicitly implements this behavior
+  it "allows shifting entries while iterating" do
+    h = { a: 1, b: 2, c: 3 }
+    visited = []
+    shifted = []
+    h.each_pair { |k,v|
+      visited << k
+      shifted << h.shift
+    }
+    visited.should == [:a, :b, :c]
+    shifted.should == [[:a, 1], [:b, 2], [:c, 3]]
+    h.should == {}
+  end
+
+  it "returns nil if the Hash is empty" do
+    h = {}
+    def h.default(key)
+      raise
+    end
+    h.shift.should == nil
+  end
+
+  it "returns nil from an empty hash" do
+    {}.shift.should == nil
+  end
+
+  it "returns nil for empty hashes with defaults and default procs" do
+    Hash.new(5).shift.should == nil
+    h = Hash.new { |*args| args }
+    h.shift.should == nil
+  end
+
+  it "preserves Hash invariants when removing the last item" do
+    h = { :a => 1, :b => 2 }
+    h.shift.should == [:a, 1]
+    h.shift.should == [:b, 2]
+    h[:c] = 3
+    h.should == {:c => 3}
+  end
+
+  it "raises a FrozenError if called on a frozen instance" do
+    -> { HashSpecs.frozen_hash.shift  }.should.raise(FrozenError)
+    -> { HashSpecs.empty_frozen_hash.shift }.should.raise(FrozenError)
+  end
+
+  it "works when the hash is at capacity" do
+    # We try a wide range of sizes in hopes that this will cover all implementations' base Hash size.
+    results = []
+    1.upto(100) do |n|
+      h = {}
+      n.times do |i|
+        h[i] = i
+      end
+      h.shift
+      results << h.size
+    end
+
+    results.should == 0.upto(99).to_a
+  end
+end