Add rough binary heap test

tests/pure_binary_heap.rs

@@ -0,0 +1,28 @@
+#[cfg(test)]
+mod tests {
+    use pyority_queue::backing::pure::{binary_heap::BinaryHeap, PureBacking};
+
+    #[test]
+    fn test_pure_binary_heap() {
+        let mut heap = BinaryHeap::new();
+        assert_eq!(heap.len(), 0);
+        heap.add(4);
+        assert_eq!(heap.len(), 1);
+        heap.add(-3);
+        assert_eq!(heap.len(), 2);
+        heap.add(6);
+        assert_eq!(heap.len(), 3);
+        heap.add(1);
+        assert_eq!(heap.len(), 4);
+        assert_eq!(heap.pop(), Some(-3));
+        assert_eq!(heap.len(), 3);
+        assert_eq!(heap.pop(), Some(1));
+        assert_eq!(heap.len(), 2);
+        assert_eq!(heap.pop(), Some(4));
+        assert_eq!(heap.len(), 1);
+        assert_eq!(heap.pop(), Some(6));
+        assert_eq!(heap.len(), 0);
+        assert_eq!(heap.pop(), None);
+        assert_eq!(heap.len(), 0);
+    }
+}