JUnit Assert.assertArrayEquals() Method Example

assertArrayEquals() method belongs to JUnit 4 org.junit.Assert class. In JUnit 5 all JUnit 4 assertion methods are moved to org.junit.jupiter.api.Assertions class.

Assert.assertArrayEquals(Object[] expecteds, Object[] actuals)

Asserts that two object arrays are equal. If they are not, an AssertionError is thrown. If expected and actual are null, they are considered equal. 
  • expecteds - Object array or array of arrays (multi-dimensional array) with expected values
  • actuals - Object array or array of arrays (multi-dimensional array) with actual values

Assert.assertArrayEquals() Method Example

Let's create concatenateStringArrays(final String[] array1, final String[] array2) method to concatenate the given String arrays into one, with overlapping array elements included twice. 
We will test concatenateStringArrays(final String[] array1, final String[] array2) method by creating JUnit test.
import org.junit.Test;

public class AssertArrayEqualsExample {
  * Concatenate the given {@code String} arrays into one, with overlapping
  * array elements included twice.
  * <p>
  * The order of elements in the original arrays is preserved.
  * @param array1
  *            the first array (can be {@code null})
  * @param array2
  *            the second array (can be {@code null})
  * @return the new array ({@code null} if both given arrays were
  *         {@code null})

 public static String[] concatenateStringArrays(final String[] array1, final String[] array2) {
     if (array1 == null || array1.length == 0) {
          return array2;
     if (array2 == null || array2.length == 0) {
          return array1;

     final String[] newArr = new String[array1.length + array2.length];
     System.arraycopy(array1, 0, newArr, 0, array1.length);
     System.arraycopy(array2, 0, newArr, array1.length, array2.length);
     return newArr;

 public void testConcatenateStringArrays() {
     final String[] input1 = new String[] { "myString2" };
     final String[] input2 = new String[] { "myString1", "myString2" };

     assertArrayEquals(input1, concatenateStringArrays(input1, null));
     assertArrayEquals(input2, concatenateStringArrays(null, input2));


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