String[] concatStringCommands(String[] firstStringArray, String[] secondStringArray) {

    if(firstStringArray == null && secondStringArray == null) {
      return secondStringArray;
    }

    else if(firstStringArray == null || firstStringArray.length == 0) {
      return secondStringArray;
    }

    else if(secondStringArray == null || secondStringArray.length == 0){
      return firstStringArray;
    }

    int len = firstStringArray.length + secondStringArray.length;

    String[] ret = new String[len];
    int idx = 0;
    for (String s : firstStringArray) {
      ret[idx] = s;
      idx++;
    }
    for (String s : secondStringArray) {
      ret[idx] = s;
      idx++;
    }
    return ret;
  }
@Test
  public void testConcatStringCommands() {
    // test one array of string as null
    assertEquals(containerExecutor.concatStringCommands(null, new String[]{"hello"})[0],
            new String[]{"hello"}[0]);
    // test both array of string as null
    Assert.assertNull(containerExecutor.concatStringCommands(null, null));
    // test case when both arrays are not null and of equal length
    String[] res = containerExecutor.concatStringCommands(new String[]{"one"},
            new String[]{"two"});
    assertEquals(res[0]+res[1], "one" + "two");
    // test both array of different length
    res = containerExecutor.concatStringCommands(new String[]{"one"},
            new String[]{"two", "three"});
    assertEquals(res[0] + res[1] + res[2], "one" + "two" + "three");

  }