Add MinStackUsingSingleStack algorithm (#5759)

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

@@ -0,0 +1,66 @@
+package com.thealgorithms.stacks;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.EmptyStackException;
+import org.junit.jupiter.api.Test;
+
+public class MinStackUsingSingleStackTest {
+
+    @Test
+    public void testBasicOperations() {
+        MinStackUsingSingleStack minStack = new MinStackUsingSingleStack();
+
+        minStack.push(3);
+        minStack.push(5);
+        assertEquals(3, minStack.getMin(), "Minimum should be 3");
+
+        minStack.push(2);
+        minStack.push(1);
+        assertEquals(1, minStack.getMin(), "Minimum should be 1");
+
+        minStack.pop();
+        assertEquals(2, minStack.getMin(), "Minimum should be 2");
+
+        minStack.pop();
+        assertEquals(3, minStack.getMin(), "Minimum should be 3");
+    }
+
+    @Test
+    public void testTopElement() {
+        MinStackUsingSingleStack minStack = new MinStackUsingSingleStack();
+
+        minStack.push(8);
+        minStack.push(10);
+        assertEquals(10, minStack.top(), "Top element should be 10");
+
+        minStack.pop();
+        assertEquals(8, minStack.top(), "Top element should be 8");
+    }
+
+    @Test
+    public void testGetMinAfterPops() {
+        MinStackUsingSingleStack minStack = new MinStackUsingSingleStack();
+
+        minStack.push(5);
+        minStack.push(3);
+        minStack.push(7);
+
+        assertEquals(3, minStack.getMin(), "Minimum should be 3");
+
+        minStack.pop(); // Popping 7
+        assertEquals(3, minStack.getMin(), "Minimum should still be 3");
+
+        minStack.pop(); // Popping 3
+        assertEquals(5, minStack.getMin(), "Minimum should now be 5");
+    }
+
+    @Test
+    public void testEmptyStack() {
+        MinStackUsingSingleStack minStack = new MinStackUsingSingleStack();
+
+        assertThrows(EmptyStackException.class, minStack::top, "Should throw exception on top()");
+        assertThrows(EmptyStackException.class, minStack::getMin, "Should throw exception on getMin()");
+    }
+}