- Added code for JUnit 5 article

junit5/src/test/java/com/baeldung/AssumptionTest.java

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+package com.baeldung;
+
+import org.junit.gen5.api.Test;
+
+import static org.junit.gen5.api.Assumptions.assumeFalse;
+import static org.junit.gen5.api.Assumptions.assumeTrue;
+import static org.junit.gen5.api.Assumptions.assumingThat;
+
+public class AssumptionTest {
+
+    @Test
+    void trueAssumption() {
+        assumeTrue(5 > 1);
+        System.out.println("Was true");
+    }
+
+    @Test
+    void falseAssumption() {
+        assumeFalse(5 < 1);
+        System.out.println("Was false");
+    }
+
+    @Test
+    void assumptionThat() {
+        String someString = "Just a string";
+        assumingThat(
+                someString.equals("Just a string"),
+                () -> System.out.println("Assumption was correct")
+        );
+    }
+}

junit5/src/test/java/com/baeldung/ExceptionTest.java

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+package com.baeldung;
+
+import org.junit.gen5.api.Test;
+
+import static org.junit.gen5.api.Assertions.assertEquals;
+import static org.junit.gen5.api.Assertions.expectThrows;
+
+public class ExceptionTest {
+
+    @Test
+    void shouldThrowException() {
+        Throwable exception = expectThrows(NullPointerException.class, null);
+        assertEquals(exception.getClass(), NullPointerException.class);
+    }
+}

junit5/src/test/java/com/baeldung/FirstTest.java

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+package com.baeldung;
+
+import org.junit.gen5.api.Test;
+
+import static org.junit.gen5.api.Assertions.assertAll;
+import static org.junit.gen5.api.Assertions.assertEquals;
+import static org.junit.gen5.api.Assertions.assertTrue;
+
+class FirstTest {
+
+    @Test
+    void lambdaExpressions() {
+        String string = "";
+        assertTrue(() -> string.isEmpty(), "String should be empty");
+    }
+
+    @Test
+    void groupAssertions() {
+        int[] numbers = {0,1,2,3,4};
+        assertAll("numbers", () -> {
+            assertEquals(numbers[0], 1);
+            assertEquals(numbers[3], 3);
+            assertEquals(numbers[4], 1);
+        });
+    }
+
+}

junit5/src/test/java/com/baeldung/NestedTest.java

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+package com.baeldung;
+
+import org.junit.gen5.api.*;
+
+import java.util.EmptyStackException;
+import java.util.Stack;
+
+public class NestedTest {
+    Stack<Object> stack;
+    boolean isRun = false;
+
+    @Test
+    @DisplayName("is instantiated with new Stack()")
+    void isInstantiatedWithNew() {
+        new Stack<Object>();
+    }
+
+    @Nested
+    @DisplayName("when new")
+    class WhenNew {
+
+        @BeforeEach
+        void init() {
+            stack = new Stack<Object>();
+        }
+
+        @Test
+        @DisplayName("is empty")
+        void isEmpty() {
+            Assertions.assertTrue(stack.isEmpty());
+        }
+
+        @Test
+        @DisplayName("throws EmptyStackException when popped")
+        void throwsExceptionWhenPopped() {
+            Assertions.expectThrows(EmptyStackException.class, () -> stack.pop());
+        }
+
+        @Test
+        @DisplayName("throws EmptyStackException when peeked")
+        void throwsExceptionWhenPeeked() {
+            Assertions.expectThrows(EmptyStackException.class, () -> stack.peek());
+        }
+
+        @Nested
+        @DisplayName("after pushing an element")
+        class AfterPushing {
+
+            String anElement = "an element";
+
+            @BeforeEach
+            void init() {
+                stack.push(anElement);
+            }
+
+            @Test
+            @DisplayName("it is no longer empty")
+            void isEmpty() {
+                Assertions.assertFalse(stack.isEmpty());
+            }
+
+            @Test
+            @DisplayName("returns the element when popped and is empty")
+            void returnElementWhenPopped() {
+                Assertions.assertEquals(anElement, stack.pop());
+                Assertions.assertTrue(stack.isEmpty());
+            }
+
+            @Test
+            @DisplayName("returns the element when peeked but remains not empty")
+            void returnElementWhenPeeked() {
+                Assertions.assertEquals(anElement, stack.peek());
+                Assertions.assertFalse(stack.isEmpty());
+            }
+        }
+    }
+}