BAEL-1588 Junit assertions (#3810)

* Added JUnit Assertions code

* Fix method spelling

* Fix wrong assertion

testing-modules/testing/src/test/java/com/baeldung/junit/AssertionsUnitTest.java

@@ -0,0 +1,101 @@
+package com.baeldung.junit;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+
+import static org.hamcrest.core.IsCollectionContaining.hasItems;
+import static org.junit.Assert.*;
+
+/**
+ * Unit test that demonstrate the different assertions available within JUnit 4
+ */
+public class AssertionsUnitTest {
+
+    @Test
+    public void whenAssertingEquality_thenEqual() {
+        String expected = "Baeldung";
+        String actual = "Baeldung";
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void whenAssertingEqualityWithMessage_thenEqual() {
+        String expected = "Baeldung";
+        String actual = "Baeldung";
+
+        assertEquals("failure - strings are not equal", expected, actual);
+    }
+
+    @Test
+    public void whenAssertingArraysEquality_thenEqual() {
+        char[] expected = { 'J', 'u', 'n', 'i', 't' };
+        char[] actual = "Junit".toCharArray();
+
+        assertArrayEquals(expected, actual);
+    }
+
+    @Test
+    public void givenNullArrays_whenAssertingArraysEquality_thenEqual() {
+        int[] expected = null;
+        int[] actual = null;
+
+        assertArrayEquals(expected, actual);
+    }
+
+    @Test
+    public void whenAssertingNull_thenTrue() {
+        Object car = null;
+
+        assertNull("The car should be null", car);
+    }
+
+    @Test
+    public void whenAssertingNotNull_thenTrue() {
+        Object car = new Object();
+
+        assertNotNull("The car should not be null", car);
+    }
+
+    @Test
+    public void whenAssertingNotSameObject_thenDifferent() {
+        Object cat = new Object();
+        Object dog = new Object();
+
+        assertNotSame(cat, dog);
+    }
+
+    @Test
+    public void whenAssertingSameObject_thenSame() {
+        Object cat = new Object();
+
+        assertSame(cat, cat);
+    }
+
+    @Test
+    public void whenAssertingConditions_thenVerified() {
+        assertTrue("5 is greater then 4", 5 > 4);
+        assertFalse("5 is not greater then 6", 5 > 6);
+    }
+
+    @Test
+    public void when_thenNotFailed() {
+        try {
+            methodThatShouldThrowException();
+            fail("Exception not thrown");
+        } catch (UnsupportedOperationException e) {
+            assertEquals("Operation Not Supported", e.getMessage());
+        }
+    }
+
+    private void methodThatShouldThrowException() {
+        throw new UnsupportedOperationException("Operation Not Supported");
+    }
+
+    @Test
+    public void testAssertThatHasItems() {
+        assertThat(Arrays.asList("Java", "Kotlin", "Scala"), hasItems("Java", "Kotlin"));
+    }
+
+}