Add the retrieval of minimum and maximum element from stack at O(1) (#5714)

src/test/java/com/thealgorithms/stacks/SmallestElementConstantTimeTest.java

@@ -0,0 +1,69 @@
+package com.thealgorithms.stacks;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.NoSuchElementException;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class SmallestElementConstantTimeTest {
+
+    private SmallestElementConstantTime sect;
+
+    @BeforeEach
+    public void setSect() {
+        sect = new SmallestElementConstantTime();
+    }
+
+    @Test
+    public void testMinAtFirst() {
+        sect.push(1);
+        sect.push(10);
+        sect.push(20);
+        sect.push(5);
+        assertEquals(1, sect.getMinimumElement());
+    }
+
+    @Test
+    public void testMinTwo() {
+        sect.push(5);
+        sect.push(10);
+        sect.push(20);
+        sect.push(1);
+        assertEquals(1, sect.getMinimumElement());
+        sect.pop();
+        assertEquals(5, sect.getMinimumElement());
+    }
+
+    @Test
+    public void testNullMin() {
+        sect.push(10);
+        sect.push(20);
+        sect.pop();
+        sect.pop();
+        assertNull(sect.getMinimumElement());
+    }
+
+    @Test
+    public void testBlankHandle() {
+        sect.push(10);
+        sect.push(1);
+        sect.pop();
+        sect.pop();
+        assertThrows(NoSuchElementException.class, () -> sect.pop());
+    }
+
+    @Test
+    public void testPushPopAfterEmpty() {
+        sect.push(10);
+        sect.push(1);
+        sect.pop();
+        sect.pop();
+        sect.push(5);
+        assertEquals(5, sect.getMinimumElement());
+        sect.push(1);
+        assertEquals(1, sect.getMinimumElement());
+    }
+}