GP-32 Fix the tdd StackTest

Author: shryhus

6-0-test-driven-development/src/test/java/com/bobocode/stack/StackTest.java

@@ -5,7 +5,7 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
-class StackTest {
+public class StackTest {
 
     private Stack<Integer> intStack = new LinkedStack<>();