Testing array length in jUnit5

I have this problem where I have to test if an array has a length of 3.

private Number[] number;

Here's my test to check if my array has a length of 3

@Test
void arrayHasALengthOf3(){
     Number[] number;

     assertTrue(number == 3);
}

I don't really know how I can solve this so can you guys help me out ...