Improve median_heap tests (#24)

.spec/data_structures/median_heap_spec.lua

@@ -1,10 +1,48 @@
 describe("Median heap", function()
 	local median_heap = require("data_structures.median_heap")
-	local heap = median_heap.new()
-	for i = 1, 100 do
-		heap:push(i)
-	end
-	assert.equal(50, heap:top())
-	assert.equal(50, heap:pop())
-	assert.equal(51, heap:pop())
+	it("constructs the correct heap when inserting sorted elements", function()
+		local heap = median_heap.new()
+		for i = 1, 100 do
+			heap:push(i)
+		end
+		assert.equal(100, heap:size())
+		assert.equal(50, heap:top())
+		assert.equal(50, heap:pop())
+		assert.equal(51, heap:pop())
+	end)
+	it("constructs the correct heap when inserting sorted elements in reverse", function()
+		local heap = median_heap.new()
+		for i = 100, 1, -1 do
+			heap:push(i)
+		end
+		assert.equal(100, heap:size())
+		assert.equal(50, heap:top())
+		assert.equal(50, heap:pop())
+		assert.equal(51, heap:pop())
+	end)
+	it("works when inserting and popping some elements", function()
+		local heap = median_heap.new()
+		heap:push(3)
+		heap:push(2)
+		heap:push(10)
+		heap:push(1)
+		heap:push(7)
+		-- Numbers in heap: 1, 2, 3, 7, 10
+		assert.equal(3, heap:top())
+		assert.equal(5, heap:size())
+		assert.equal(3, heap:pop())
+		-- Numbers in heap: 1, 2, 7, 10
+		assert.equal(4, heap:size())
+		assert.equal(2, heap:pop())
+		-- Numbers in heap: 1, 7, 10
+		assert.equal(3, heap:size())
+		assert.equal(7, heap:pop())
+		-- Numbers in heap: 1, 10
+		assert.equal(2, heap:size())
+		assert.equal(1, heap:pop())
+		-- Numbers in heap: 10
+		assert.equal(1, heap:size())
+		assert.equal(10, heap:pop())
+		assert.equal(0, heap:size())
+	end)
 end)