Add JUnit tests for priority queue data structure (#3778)

src/test/java/com/thealgorithms/datastructures/queues/PriorityQueuesTest.java

@@ -0,0 +1,58 @@
+package com.thealgorithms.datastructures.queues;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class PriorityQueuesTest {
+
+    @Test
+    void testPQInsertion() {
+        PriorityQueue myQueue = new PriorityQueue(4);
+        myQueue.insert(2);
+        Assertions.assertEquals(myQueue.peek(), 2);
+
+        myQueue.insert(5);
+        myQueue.insert(3);
+        Assertions.assertEquals(myQueue.peek(), 5);
+
+        myQueue.insert(10);
+        Assertions.assertEquals(myQueue.peek(), 10);
+    }
+
+    @Test
+    void testPQDeletion() {
+        PriorityQueue myQueue = new PriorityQueue(4);
+        myQueue.insert(2);
+        myQueue.insert(5);
+        myQueue.insert(3);
+        myQueue.insert(10);
+        
+        myQueue.remove();
+        Assertions.assertEquals(myQueue.peek(), 5);
+        myQueue.remove();
+        myQueue.remove();
+        Assertions.assertEquals(myQueue.peek(), 2);
+    }
+
+    @Test
+    void testPQExtra() {
+        PriorityQueue myQueue = new PriorityQueue(4);
+        Assertions.assertEquals(myQueue.isEmpty(), true);
+        Assertions.assertEquals(myQueue.isFull(), false);
+        myQueue.insert(2);
+        myQueue.insert(5);
+        Assertions.assertEquals(myQueue.isFull(), false);
+        myQueue.insert(3);
+        myQueue.insert(10);
+        Assertions.assertEquals(myQueue.isEmpty(), false);
+        Assertions.assertEquals(myQueue.isFull(), true);
+        
+        myQueue.remove();
+        Assertions.assertEquals(myQueue.getSize(), 3);
+        Assertions.assertEquals(myQueue.peek(), 5);
+        myQueue.remove();
+        myQueue.remove();
+        Assertions.assertEquals(myQueue.peek(), 2);
+        Assertions.assertEquals(myQueue.getSize(), 1);
+    }
+}