Write initial version of the library.

spec/heap_spec.cr

@@ -0,0 +1,44 @@
+require "./spec_helper"
+
+describe Array do
+  describe "#heapify" do
+    it "preserves the elements in the array" do
+      a = Array(Int32).new(20) { rand(10) }
+      a.sort.should eq(a.clone.heapify!.sort)
+    end
+
+    it "creates an array with proper ordering" do
+      a = Array(Int32).new(20) { rand(10) }
+      a.heapify!
+      a.is_heap?.should be_true
+    end
+
+    it "maintains heap property while popping" do
+      a = Array(Int32).new(20) { rand(10) }
+      a.heapify!
+      20.times do |i|
+        a.heap_pop
+        a.is_heap?.should be_true
+      end
+    end
+
+    it "maintains heap property while pushing" do
+      a = [] of Int32
+      20.times do 
+        a.heap_push(rand 10)
+        a.is_heap?.should be_true
+      end
+    end
+
+    it "pops numbers in descending order" do
+      a = Array(Int32).new(20) { rand(10) }
+      a.heapify!
+      last = Int32::MAX
+      20.times do
+        popped = a.heap_pop
+        popped.should be <= last
+        last = popped
+      end
+    end
+  end
+end