feat: stack unit test

Author: yeoshuheng

test/dataStructures/stack/StackTest.java

@@ -0,0 +1,32 @@
+package test.dataStructures.stack;
+
+import org.junit.Assert;
+import org.junit.Test;
+import src.dataStructures.stack.Stack;
+public class StackTest {
+    @Test
+    public void testEmpty(){
+        Stack<Integer> stk = new Stack<>();
+        Assert.assertEquals(stk.pop(), null);
+        Assert.assertEquals(stk.peek(), null);
+    }
+
+    @Test
+    public void testPopAndPeek() {
+        Stack<Integer> stk = new Stack<>(1, 2, 3);
+        Assert.assertEquals(stk.peek().toString(), "3");
+        Assert.assertEquals(stk.pop().toString(), "3");
+        Assert.assertEquals(stk.peek().toString(), "2");
+    }
+
+    @Test
+    public void testPush() {
+        Stack<Integer> stk = new Stack<>();
+        stk.push(1);
+        Assert.assertEquals(stk.peek().toString(), "1");
+        stk.push(2);
+        stk.push(3);
+        Assert.assertEquals(stk.peek().toString(), "3");
+    }
+
+}